Upgrade flutter to 1.20

Fixes #131

pubspec.lock

@@ -7,14 +7,14 @@ packages:
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.1"
+    version: "6.0.0"
   analyzer:
     dependency: transitive
     description:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.39.2+1"
+    version: "0.39.16"
   archive:
     dependency: transitive
     description:
@@ -42,7 +42,7 @@ packages:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.4.1"
+    version: "2.4.2"
   auto_size_text:
     dependency: "direct main"
     description:
@@ -85,6 +85,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.2.0+1"
+  characters:
+    dependency: transitive
+    description:
+      name: characters
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.0"
   charcode:
     dependency: transitive
     description:
@@ -92,6 +99,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.3"
+  cli_util:
+    dependency: transitive
+    description:
+      name: cli_util
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.1.4"
   clock:
     dependency: transitive
     description:
@@ -105,7 +119,7 @@ packages:
       name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.12"
+    version: "1.14.13"
   colorize:
     dependency: transitive
     description:
@@ -140,7 +154,7 @@ packages:
       name: crypto
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.4"
+    version: "2.1.5"
   csslib:
     dependency: transitive
     description:
@@ -206,13 +220,20 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.1"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.1.0"
   file:
     dependency: transitive
     description:
       name: file
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "5.1.0"
+    version: "5.2.1"
   fimber:
     dependency: "direct main"
     description:
@@ -468,7 +489,7 @@ packages:
       name: json_rpc_2
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0"
+    version: "2.2.1"
   launch_review:
     dependency: "direct main"
     description:
@@ -498,7 +519,7 @@ packages:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.6"
+    version: "0.12.8"
   meta:
     dependency: transitive
     description:
@@ -513,13 +534,6 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.9.6+3"
-  multi_server_socket:
-    dependency: transitive
-    description:
-      name: multi_server_socket
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.0.2"
   mutex:
     dependency: "direct main"
     description:
@@ -575,7 +589,7 @@ packages:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.4"
+    version: "1.7.0"
   path_provider:
     dependency: transitive
     description:
@@ -645,7 +659,7 @@ packages:
       name: process
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.0.12"
+    version: "3.0.13"
   provider:
     dependency: "direct main"
     description:
@@ -832,7 +846,7 @@ packages:
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "1.9.5"
   steel_crypt:
     dependency: "direct main"
     description:
@@ -881,21 +895,21 @@ packages:
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.4"
+    version: "1.15.2"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.15"
+    version: "0.2.17"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.4"
+    version: "0.3.10"
   tool_base:
     dependency: transitive
     description:
@@ -930,7 +944,7 @@ packages:
       name: typed_data
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.6"
+    version: "1.2.0"
   url_launcher:
     dependency: "direct main"
     description:
@@ -1044,5 +1058,5 @@ packages:
     source: hosted
     version: "0.0.6"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.9.0-14.0.dev <3.0.0"
   flutter: ">=1.17.0 <2.0.0"