Upgrade to Java 1.7 where possible.

briar-android-tests/build.gradle

 apply plugin: 'com.android.library'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.7
+targetCompatibility = 1.7
 apply plugin: 'witness'
 apply plugin: 'com.neenbedankt.android-apt'
 

briar-android/build.gradle

@@ -104,8 +104,8 @@ android {
 	}
 
 	compileOptions {
-		sourceCompatibility JavaVersion.VERSION_1_6
-		targetCompatibility JavaVersion.VERSION_1_6
+		sourceCompatibility JavaVersion.VERSION_1_7
+		targetCompatibility JavaVersion.VERSION_1_7
 	}
 
 	lintOptions {

briar-desktop/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.7
+targetCompatibility = 1.7
 
 apply plugin: 'witness'
 

briar-tests/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.7
+targetCompatibility = 1.7
 
 apply plugin: 'witness'