Ensure gradle build files are set to Java 7

complete/build.gradle

@@ -18,6 +18,8 @@ jar {
     baseName = 'gs-messaging-stomp-websocket'
     version =  '0.1.0'
 }
+sourceCompatibility = 1.7
+targetCompatibility = 1.7
 
 repositories {
     mavenLocal()

initial/build.gradle

@@ -18,6 +18,8 @@ jar {
     baseName = 'gs-messaging-stomp-websocket'
     version =  '0.1.0'
 }
+sourceCompatibility = 1.7
+targetCompatibility = 1.7
 
 repositories {
     mavenLocal()