build: Update version of compile SDK and build tools

Change-Id: Id2e2f944b9cbc4a374714b1173a5aef349986bf9
diff --git a/app/build.gradle b/app/build.gradle
index a18648d..5c1b90b 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -3,8 +3,8 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 21
-    buildToolsVersion "21.1.2"
+    compileSdkVersion 23
+    buildToolsVersion "23.0.2"
 
     defaultConfig {
         applicationId "net.named_data.nfd"
@@ -135,8 +135,8 @@
 
 dependencies {
     compile fileTree(dir: 'libs', include: ['*.jar'])
-    compile 'com.android.support:appcompat-v7:21.0.3'
-    compile 'com.android.support:support-v4:21.0.3'
+    compile 'com.android.support:appcompat-v7:23.1.1'
+    compile 'com.android.support:support-v4:23.1.1'
 
     compile('com.intel.jndn.management:jndn-management:1.1.0') {
       exclude group: 'net.named-data', module: 'jndn'