Use two cores for gradle

Makefile

@@ -100,7 +100,7 @@ android:
 	cp build/android/out/$(BUILDTYPE)/ca-bundle.crt android/java/lib/src/main/assets/ca-bundle.crt && \
 	cp -r build/android/out/$(BUILDTYPE)/styles android/java/lib/src/main/assets/styles && \
 	cd android/java && \
-	./gradlew build
+	./gradlew --parallel-threads=$(JOBS) build
 
 ##### Test cases ###############################################################
 

android/java/app/build.gradle

@@ -4,6 +4,10 @@ android {
     compileSdkVersion 21
     buildToolsVersion "21.1.2"
 
+    repositories {
+        jcenter()
+    }
+
     defaultConfig {
         applicationId "com.mapbox.mapboxgl.app"
         minSdkVersion 14

android/java/build.gradle

@@ -7,9 +7,3 @@ buildscript {
         classpath 'com.android.tools.build:gradle:1.0.0-rc4'
     }
 }
-
-allprojects {
-    repositories {
-        jcenter()
-    }
-}

android/java/lib/build.gradle

@@ -4,6 +4,10 @@ android {
     compileSdkVersion 21
     buildToolsVersion "21.1.2"
 
+    repositories {
+        jcenter()
+    }
+
     defaultConfig {
         minSdkVersion 14
         targetSdkVersion 21