chore: add api-report check to travis (#8023)

.travis.yml

@@ -7,6 +7,9 @@ script:
 - npm run setup
 - npm run unit-test
 
+# public API changes check
+- npm run api-extractor-ci
+
 # circular references check
 - cd tests && npm i
 - node_modules/.bin/webpack --env.android

CONTRIBUTING.md

@@ -69,6 +69,7 @@ git checkout -b <my-fix-branch> master
     - Rebase your changes to the latest master: `git pull --rebase upstream master`.
     - Ensure all unit test are green for Android and iOS. Check [running unit tests](DevelopmentWorkflow.md#running-unit-tests).
     - Ensure your changes pass tslint validation. (run `npm run tslint` in the root of the repo).
+    - If you've made changes to a public API, make sure you update and add the `api-reports/NativeScript.api.md` file to the PR. (run `npm run api-extractor` to update the api-report and definitions).
 
 6. Push your fork. If you have rebased you might have to use force-push your branch:
 ```

package.json

@@ -47,6 +47,7 @@
     "unit-test-watch": "mocha-typescript-watch -p unit-tests/tsconfig.json --opts unit-tests/mocha.opts",
     "dev-link-tns-core-modules-widgets": "(cd tns-core-modules-widgets/dist/package && npm link) && (cd nativescript-core && npm i ../tns-core-modules-widgets/dist/package --save)",
     "api-extractor": "api-extractor run --local --verbose && (cd nativescript-core && cat nativescript-core.header nativescript-core.d.ts > tmp_file && mv tmp_file nativescript-core.d.ts)",
+    "api-extractor-ci": "api-extractor run --verbose",
     "typedoc": "npm run api-extractor && typedoc --tsconfig tsconfig.typedoc.json",
     "typedoc-dev": "npm run typedoc && cd bin/dist/apiref && npx http-server",
     "build-core": "sh ./build/build-core.sh",