Fix month index when converting Date to java.util.Date

In **toDate** method of **net.sf.marineapi.nmea.util.Date** class the wrong index of month is being used. It must be 0 based - [link to Oracle docs.](http://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#MONTH)
In constructor month value is incremented but not decremented when converting back.