Fix travis build for gradle upgrade

Signed-off-by: Aron Heinecke <aron.heinecke@t-online.de>

Author: 0xpr03

.travis.yml

@@ -13,7 +13,7 @@ android:
     - build-tools-28.0.3
 
     # The SDK version used to compile your project
-    - android-27
+    - android-28
 
     # Additional components
     - extra-android-m2repository