Fixed firebase regression in AndroidGradleBuilder.

Author: shannah

maven/codenameone-maven-plugin/src/main/java/com/codename1/builders/AndroidGradleBuilder.java

@@ -1168,11 +1168,22 @@ public void usesClassMethod(String cls, String method) {
                 debug("Adding firebase core to gradle dependencies.");
                 debug("Play services version: " + request.getArg("var.android.playServicesVersion", ""));
                 debug("gradleDependencies before: "+request.getArg("gradleDependencies", ""));
-                request.putArgument("gradleDependencies", request.getArg("gradleDependencies", "") + "\n"+compile+" \"com.google.firebase:firebase-core:${var.android.firebaseCoreVersion}\"\n");
+
+                request.putArgument(
+                        "gradleDependencies",
+                        request.getArg("gradleDependencies", "") +
+                                "\n"+compile+" \"com.google.firebase:firebase-core:" +
+                                request.getArg("android.firebaseCoreVersion", playServicesVersion) + "\"\n"
+                );
                 debug("gradleDependencies after: "+request.getArg("gradleDependencies", ""));
             }
             if (!request.getArg("gradleDependencies", "").contains("com.google.firebase:firebase-messaging")) {
-                request.putArgument("gradleDependencies", request.getArg("gradleDependencies", "") + "\n"+compile+" \"com.google.firebase:firebase-messaging:${var.android.firebaseMessagingVersion}\"\n");
+                request.putArgument(
+                        "gradleDependencies",
+                        request.getArg("gradleDependencies", "") +
+                                "\n"+compile+" \"com.google.firebase:firebase-messaging:" +
+                                request.getArg("android.firebaseMessagingVersion", playServicesVersion) + "\"\n"
+                );
             }
         }