Add javaDoc for MultipartUtility.close()

Author: nitzanj

cloudinary-android/src/main/java/com/cloudinary/android/MultipartUtility.java

@@ -136,6 +136,10 @@ public HttpURLConnection execute() throws IOException {
         return httpConn;
     }
 
+    /***
+     * Closes the internal connection's output stream.
+     * Closing a previously closed stream has no effect.
+     */
     public void close(){
         if (writer != null){
             writer.close();