SDL: updated Gradle build files

project/build.gradle

@@ -1,18 +1,26 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
+
 buildscript {
+
     repositories {
+        google()
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.0'
+        classpath 'com.android.tools.build:gradle:3.2.1'
+
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
     }
 }
 
 allprojects {
     repositories {
+        google()
         jcenter()
-        maven {
-            url "https://maven.google.com"
-        }
-     }
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
 }