Fix appium#924 (appium#951)

* Fix appium#924 * address review comments

Author: SrinivasanTarget

src/main/java/io/appium/java_client/remote/NewAppiumSessionPayload.java

@@ -264,21 +264,23 @@ public void writeTo(Appendable appendable) throws IOException {
  json.name(DESIRED_CAPABILITIES);
  json.write(first);
 
- // And write the first capability for gecko13
- json.name(CAPABILITIES);
- json.beginObject();
+ if (!forceMobileJSONWP) {
+ // And write the first capability for gecko13
+ json.name(CAPABILITIES);
+ json.beginObject();
 
- json.name(ALWAYS_MATCH);
- getW3C().forEach(json::write);
- 
- json.name(FIRST_MATCH);
- json.beginArray();
- //noinspection unchecked
- json.beginObject();
- json.endObject();
- json.endArray();
+ json.name(ALWAYS_MATCH);
+ getW3C().forEach(json::write);
 
- json.endObject(); // Close "capabilities" object
+ json.name(FIRST_MATCH);
+ json.beginArray();
+ //noinspection unchecked
+ json.beginObject();
+ json.endObject();
+ json.endArray();
+
+ json.endObject(); // Close "capabilities" object
+ }
 
  writeMetaData(json);