Use build-plugin 3.1.2

build.gradle

@@ -8,12 +8,13 @@ buildscript {
 
     repositories {
         jcenter()
+	google()
         maven { url 'https://jitpack.io' }
     }
 
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath 'com.android.tools.build:gradle:2.3.3'
+        classpath 'com.android.tools.build:gradle:3.1.2'
         classpath 'com.stanfy.spoon:spoon-gradle-plugin:1.2.2'
         classpath 'com.github.ben-manes:gradle-versions-plugin:0.17.0'
         classpath 'de.mobilej.unmock:UnMockPlugin:0.6.4'