Add "GN" NMEA TalkerID support for GPS driver

[sam1016yu]

In gps/NmeaParser.java, line 48-51, for the message type identifier, some devices use "GN" instead of "GP" as TalkerID, it's better to support that as well. In that case, identifiers will look like

    // NMEA Message Types
    private static final String GGA = "GNGGA";
    private static final String GSV = "GNGSV";
    private static final String GLL = "GNPGLL";
    private static final String RMC = "GNRMC";

[PaulTR]

Google isn't actively supporting this right now, so your best bet would be to make the changes yourself and submit the pr