removed update_isotopes when position using a numerical value
removed update_isotopes when position using a numerical value

USGSDenverPychron/pychron,NMGRL/pychron,NMGRL/pychron,NMGRL/pychron,UManPychron/pychron,UManPychron/pychron,USGSDenverPychron/pychron,UManPychron/pychron,USGSDenverPychron/pychron,UManPychron/pychron,NMGRL/pychron,USGSDenverPychron/pychron