Changed API version and everything else required.

(cherry picked from commit db1a282)

.travis.yml

@@ -16,10 +16,10 @@ android:
     - tools
 
     # The BuildTools version used by your project
-    - build-tools-26.0.2
+    - build-tools-27.0.3
 
     # The SDK version used to compile your project
-    - android-25
+    - android-27
 
     # Additional components
     - extra-android-m2repository