Update build tools and platform in travis.yml

Author: manas-chaudhari

.travis.yml

@@ -4,8 +4,8 @@ android:
   components:
     - tools
     - platform-tools
-    - build-tools-25.0.2
-    - android-25
+    - build-tools-27.0.3
+    - android-27
     - extra-android-m2repository
     - sys-img-armeabi-v7a-android-19
 jdk:
@@ -25,4 +25,4 @@ cache:
   directories:
     - $HOME/.gradle/caches/
     - $HOME/.gradle/wrapper/
-    - $HOME/.android/build-cache
+    - $HOME/.android/build-cache