Ensure Java 1.7 compatibility for pre-NYC platforms

Change-Id: I2dd3a4c4c4772aa29098bb8576a5bd22c04db5e5
diff --git a/annotations/build.gradle b/annotations/build.gradle
index 2ff9980..75951e8 100644
--- a/annotations/build.gradle
+++ b/annotations/build.gradle
@@ -6,6 +6,9 @@
     main.java.srcDir 'src'
 }
 
+sourceCompatibility = JavaVersion.VERSION_1_7
+targetCompatibility = JavaVersion.VERSION_1_7
+
 jar {
     from sourceSets.main.output
 }