Use the gradle-versions-plugin to determine outdated dependencies

Run it like

    $ ./gradlew dependencyUpdates

For more details see https://github.com/ben-manes/gradle-versions-plugin.

Change-Id: I6094bfbc3ee3cc2c5fe21c59fdb2fc6a0b9330ae
diff --git a/README b/README
index 223e745..10198de 100644
--- a/README
+++ b/README
@@ -122,3 +122,11 @@
 
 Note that we do not accept Pull Requests via the Github mirror.
 
+## Build-time dependencies
+
+The app uses the following build-time dependencies provided under the given licenses:
+
+* Apache License, Version 2.0
+  * [gradle-versions-plugin](https://github.com/ben-manes/gradle-versions-plugin)
+
+Compile-time dependencies are listed in the app's help screen.
diff --git a/build.gradle b/build.gradle
index e0b366a..2f90a61 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,11 +1,14 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
+apply plugin: 'com.github.ben-manes.versions'
+
 buildscript {
     repositories {
         jcenter()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:1.5.0'
+        classpath 'com.github.ben-manes:gradle-versions-plugin:0.12.0'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files