fix keyerror when generate RTS_GMLC.m

[sablea]

There is an error in the variable name in the script.py file in the RTS_Data/FormattedData/MATPOWER folder. "g['Start Heat Cold MMBTU']" should be written as "g['Start Heat Cold MBTU'] ". I have fixed this error so that cli.py can run correctly and generate RTS_GMLC.m. #154