Fix missing Gradle repo for RuntimePermissions

Top-level Gradle repository for this project was missing, preventing
build from working correctly.

Bug: 67615229
Test: manual build
Change-Id: Iab855157f8f11c61dadb3f8e0d31e6447d6be0cf
diff --git a/system/RuntimePermissions/build.gradle b/system/RuntimePermissions/build.gradle
index 2c20fc4..d473b34 100644
--- a/system/RuntimePermissions/build.gradle
+++ b/system/RuntimePermissions/build.gradle
@@ -1,5 +1,8 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 buildscript {
+  repositories {
+    jcenter()
+  }
   dependencies {
     classpath 'com.android.tools.build:gradle:2.3.3'
   }