Merge remote-tracking branch 'origin/master'

.travis.yml

+language: android
+#### use android since there are android components####
+jdk:
+  - openjdk11
+
+android:
+  components:
+    - build-tools-29
+    - android-29
+    - extra
+
+licenses:
+  - 'android-sdk-license-.+'
+  - 'google-gdk-license-.+'
+  - 'android-sdk-preview-license-.+'
+
+
+install: true
+
+sudo: required
+before_script:
+  - chmod +x gradlew
+
+script:
+  - ./gradlew clean build -i --continue
+