[script] update make-pretty to bash (#4698)

- Also update CONTRIBUTING.md and STYLE_GUIDE.md.

CONTRIBUTING.md

@@ -109,7 +109,7 @@ This will open up a text editor where you can specify which commits to squash.
 
 #### Coding Conventions and Style
 
-OpenThread uses and enforces the [OpenThread Coding Conventions and Style](STYLE_GUIDE.md) on all code, except for code located in [third_party](third_party).  Use the `script/make-pretty` and `script/make-pretty check` targets to automatically reformat code and check for code-style compliance, respectively.  OpenThread currently requires [clang-format v6.0.0](http://releases.llvm.org/download.html#6.0.0) and [yapf](https://github.com/google/yapf) for `script/make-pretty` and `script/make-pretty check`.
+OpenThread uses and enforces the [OpenThread Coding Conventions and Style](STYLE_GUIDE.md) on all code, except for code located in [third_party](third_party).  Use `script/make-pretty` and `script/make-pretty check` to automatically reformat code and check for code-style compliance, respectively.  OpenThread currently requires [clang-format v6.0.0](http://releases.llvm.org/download.html#6.0.0) for C/C++ and [yapf](https://github.com/google/yapf) for Python.
 
 As part of the cleanup process, you should also run `script/make-pretty check` to ensure that your code passes the baseline code style checks.
 

STYLE_GUIDE.md

@@ -114,9 +114,9 @@
 
 ## Format and Style
 
-- OpenThread uses the `make pretty` build target to reformat code and enforce code format and style.  The `make pretty-check` build target is included in OpenThread's continuous integration and must pass before a pull request is merged.
+- OpenThread uses `script/make-pretty` to reformat code and enforce code format and style.  `script/make-pretty check` build target is included in OpenThread's continuous integration and must pass before a pull request is merged.
 
-- The `make pretty` and `make pretty-check` build targets require [clang-format v6.0.0](http://releases.llvm.org/download.html#6.0.0).
+- `script/make-pretty` requires [clang-format v6.0.0](http://releases.llvm.org/download.html#6.0.0) for C/C++ and [yapf](https://github.com/google/yapf) for Python.
 
 ### File Names
 - File names should match the names and types of what is described in the file.  If a file contains many declarations and definitions, the author should choose the one that predominantly describes or that makes the most sense.

script/clang-format

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 #  Copyright (c) 2018, The OpenThread Authors.
 #  All rights reserved.

script/clang-format-check

@@ -45,6 +45,6 @@ die() {
 
 for file in "$@"; do
     echo "Checking ${file}"
-    "$(dirname "$0")"/clang-format.sh -style=file "${file}" | diff -u "${file}" - || die "${file} is not pretty."
+    "$(dirname "$0")"/clang-format -style=file "${file}" | diff -u "${file}" - || die "${file} is not pretty."
     [ -z "$(tail -c1 "${file}")" ] || die "${file} misses EOF newline."
 done

script/make-pretty

@@ -62,7 +62,7 @@ do_clang_format()
     echo -e '====================='
 
     git ls-files "${OT_CLANG_SOURCES[@]}" | grep -E "^($(echo "${OT_CLANG_DIRS[@]}" | tr ' ' '|'))" \
-        | xargs -n3 -P"${OT_BUILD_JOBS}" script/clang-format.sh -style=file -i -verbose
+        | xargs -n3 -P"${OT_BUILD_JOBS}" script/clang-format -style=file -i -verbose
 }
 
 do_clang_check()
@@ -72,7 +72,7 @@ do_clang_check()
     echo -e '====================='
 
     git ls-files "${OT_CLANG_SOURCES[@]}" | grep -E "^($(echo "${OT_CLANG_DIRS[@]}" | tr ' ' '|'))" \
-        | xargs -n3 -P"${OT_BUILD_JOBS}" script/clang-format-check.sh
+        | xargs -n3 -P"${OT_BUILD_JOBS}" script/clang-format-check
 }
 
 do_python_format()