Ensure Java 1.7 compatibility for pre-NYC platforms

Change-Id: I2dd3a4c4c4772aa29098bb8576a5bd22c04db5e5
diff --git a/v13/build.gradle b/v13/build.gradle
index c1e624b..d7eddbb 100644
--- a/v13/build.gradle
+++ b/v13/build.gradle
@@ -51,6 +51,9 @@
     compile files(internalJar.archivePath)
 }
 
+sourceCompatibility = JavaVersion.VERSION_1_7
+targetCompatibility = JavaVersion.VERSION_1_7
+
 android {
     compileSdkVersion 13
 
@@ -60,7 +63,6 @@
         //targetSdkVersion 19
     }
 
-
     sourceSets {
         main.manifest.srcFile 'AndroidManifest.xml'
         main.java.srcDirs = ['java']
@@ -70,6 +72,11 @@
         androidTest.java.srcDir 'tests/java'
     }
 
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_7
+        targetCompatibility JavaVersion.VERSION_1_7
+    }
+
     lintOptions {
         // TODO: fix errors and reenable.
         abortOnError false