Fixed unresolved dependency by JCenter
Fixed unresolved dependency by JCenter

Problem:
* What went wrong:
A problem occurred configuring root project 'TapTargetView'.
> Could not resolve all artifacts for configuration ':classpath'.
   > Could not find aapt2-proto.jar (com.android.tools.build:aapt2-proto:0.3.1).
     Searched in the following locations:
         https://jcenter.bintray.com/com/android/tools/build/aapt2-proto/0.3.1/aapt2-proto-0.3.1.jar

Changing google to the first source for dependencies resolves this issue

KeepSafe/TapTargetView