Fix input file error message

[forsyth2]

Fix input file error message. Resolves #125.

[forsyth2]

Tested by setting years = "1500:1502:2", (e.g., years that would not be in the data) for [climo] [[ atm_monthly_diurnal_8xdaily_180x360_aave ]] and [ts] [[ atm_monthly_180x360_aave ]].

[forsyth2]

The issue was that if ls {{ case }}.{{ input_files }}.????-*.nc does not match any files, then input.txt will be filled with files ending in *.nc rather than actual input files. Thus, we run grep on the *.