Change mavenCentral -> jcenter

Ref: https://blog.bintray.com/2015/02/09/android-studio-migration-from-maven-central-to-jcenter/

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135211072

build.gradle

@@ -16,7 +16,6 @@
 
 buildscript {
     repositories {
-        mavenCentral()
         jcenter()
     }
     dependencies {
@@ -27,7 +26,7 @@ buildscript {
 
 allprojects {
     repositories {
-        mavenCentral()
+        jcenter()
     }
     project.ext {
         compileSdkVersion=24