Add --canary flag to gradle project test and update gradle.

This flag enables support for Android Studio 3.0 which allows us to use
Java 8 features. Gradle is updated to version 4.1.0.

BUG=webrtc:8084

Review-Url: https://codereview.webrtc.org/2994123002
Cr-Commit-Position: refs/heads/master@{#19319}
diff --git a/webrtc/examples/androidtests/gradle_project_test.py b/webrtc/examples/androidtests/gradle_project_test.py
index 9a0621b..1f04960 100644
--- a/webrtc/examples/androidtests/gradle_project_test.py
+++ b/webrtc/examples/androidtests/gradle_project_test.py
@@ -64,7 +64,7 @@
     _RunCommand([GENERATE_GRADLE_SCRIPT, '--output-directory', output_dir,
         '--target', '//webrtc/examples:AppRTCMobile',
         '--project-dir', project_dir,
-        '--use-gradle-process-resources', '--split-projects'])
+        '--use-gradle-process-resources', '--split-projects', '--canary'])
     _RunCommand([GRADLEW_BIN, 'assembleDebug'], project_dir)
   finally:
     # Do not delete temporary directory if user specified it manually.