Update PULL_REQUEST_TESTS.md (NativeScript#185)

Add a record for `tests-app-ng`.

Author: Vasil Chimev

PULL_REQUEST_TESTS.md

@@ -8,3 +8,4 @@ This document describes comment messages available to execute tests on pull requ
 |`ng`|ci/jenkins/webpack-ng|Pack the *nativescript-dev-webpack* plugin and bundle the [template-hello-world-ng](https://github.com/NativeScript/template-hello-world-ng) template app.|
 |`groceries`|ci/jenkins/webpack-groceries|Pack the *nativescript-dev-webpack* plugin and bundle the [Groceries](https://github.com/NativeScript/sample-Groceries) app.                |
 |`sdk`|ci/jenkins/webpack-sdk|Pack the *nativescript-dev-webpack* plugin and bundle the [SDK](https://github.com/NativeScript/nativescript-sdk-examples-ng) app.                      |
+|`testsappng`|ci/jenkins/webpack-testsappng|Pack the *nativescript-dev-webpack* plugin and bundle the [tests-app-ng](https://github.com/NativeScript/tests-app-ng) app.                    |