Bump com.github.dcendents:android-maven-gradle-plugin from 1.5 to 2.1

Bumps [com.github.dcendents:android-maven-gradle-plugin](https://github.com/dcendents/android-maven-gradle-plugin) from 1.5 to 2.1.
- [Release notes](https://github.com/dcendents/android-maven-gradle-plugin/releases)
- [Commits](dcendents/android-maven-gradle-plugin@1.5...2.1)

---
updated-dependencies:
- dependency-name: com.github.dcendents:android-maven-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -12,7 +12,7 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:2.3.+'
-        classpath 'com.github.dcendents:android-maven-gradle-plugin:1.5'
+        classpath 'com.github.dcendents:android-maven-gradle-plugin:2.1'
     }
 }