Gradle: Upgrade to the latest Android plugin

Version 2.2.0 has built-in support for bootstrapping the SDK, so we can
drop Jake Wharton's deprecated sdk-manager-plugin.

Change-Id: I7194977e0c09b13d616c046dd08e6b99d1712e8d
diff --git a/README.md b/README.md
index c42aa1a..08d4b7d 100644
--- a/README.md
+++ b/README.md
@@ -126,7 +126,6 @@
 
 * Apache License, Version 2.0
   * [gradle-versions-plugin](https://github.com/ben-manes/gradle-versions-plugin)
-  * [sdk-manager-plugin](https://github.com/JakeWharton/sdk-manager-plugin)
 
 * The MIT License
   * [jitpack.io](https://github.com/jitpack/jitpack.io)
diff --git a/app/build.gradle b/app/build.gradle
index 69123dc..722d4c6 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -1,4 +1,3 @@
-apply plugin: 'android-sdk-manager'
 apply plugin: 'com.android.application'
 
 android {
diff --git a/build.gradle b/build.gradle
index 37df852..51411b1 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,12 +12,9 @@
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:1.5.0'
+        classpath 'com.android.tools.build:gradle:2.2.0'
         classpath 'com.github.ben-manes:gradle-versions-plugin:0.12.0'
 
-        // Use an unreleased version via JitPack.
-        classpath 'com.github.JakeWharton:sdk-manager-plugin:1d29782'
-
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
     }