Clean up ignored files

build.gradle

@@ -1,6 +1,7 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
+    ext.kotlin_version = '1.3.10'
     ext {
         supportLibVersion = '1.0.0'
         firebase = "11.8.0"
@@ -14,6 +15,7 @@ buildscript {
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.2.1'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }