Update pmedian.py

[Otaola93]

the name in the tag has to match the name in the string data='pmedian'

[merrickj]

For this to work with MOS as currently constructed, if tag is changed to pmedian, then line 77 would have to become pmedian = 'pmedian.dat'. Similarly tag could by changed to xyz and then line 77 would be required to be xyz = 'pmedian.dat'. Note that when the MOSBackend parses the file and subsequently creates the model recipe, it will regenerate this line 77 to whatever input file the user uploads to MOS.

The MOS cvxpy kernel requires the input file object to be an actual input file object, while the Pyomo kernel only requires the filename. This will be reconciled in forthcoming update of Pyomo kernel.