Update to Android Gradle Plugin 3.1 (#77)

Author: Marcel Schnelle

.idea/runConfigurations/Instrumentation_Library__Run_Instrumented_Tests.xml

@@ -32,7 +32,7 @@ INSTRUMENTATION_MIN_SDK_VERSION             = 26
 INSTRUMENTATION_RUNNER_MIN_SDK_VERSION      = 14
 
 # Dependency versions (plugins)
-ANDROID_PLUGIN_VERSION                      = 3.0.1
+ANDROID_PLUGIN_VERSION                      = 3.1.0
 BINTRAY_PLUGIN_VERSION                      = 1.8.0
 SHADOW_PLUGIN_VERSION                       = 2.0.1
 VERSIONS_PLUGIN_VERSION                     = 0.17.0