add javadoc to a method in android/GT_APP/app/src/main/java/com/tencent/wstt/gt/plugin/gps/GTGPSUtils.java

Hi there, when I was reading the code of the function "private static float getDistance(double lat1, double lon1, double lat2, double lon2)" in android/GT_APP/app/src/main/java/com/tencent/wstt/gt/plugin/gps/GTGPSUtils.java, I found it has no Javadoc. I would like to contribute by adding “return   euclidean distance between points". Can you please check if this is correct? Thanks.
