Fix adding maven to repositories

[vtrifonov]

There are currently two problems with adding maven to the repositories.

1. When adding it to the platforms/android/build.gradle we need to add it before the closing } but not after it, that's why I'm subtracting 1 from the index and size of the matched block:

search = (buildGradleContent.indexOf(repositories[0]) - 1) + (repositories[0].length - 1);

2. In the latest version of platforms/android/app/build.gradle in the repositories section we don't need to add the maven repository as it is already added in the platforms/android/build.gradle file.