Gaussian: fix parsing of platform line

[berquist]

Closes #1420

cclib/cclib-data#190 should be merged after this PR.

[berquist]

This is failing because the regression testing code no longer allows defining a test that's missing a file. Since this is a common scenario with PRs made to both repos simultaneously, I could change it back to the previous behavior...or we merge cclib-data PRs with the understanding that the next cclib PR has to be the regression fix.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.38%. Comparing base (17e3b62) to head (b55526d).
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1452   +/-   ##
=======================================
  Coverage   81.38%   81.38%           
=======================================
  Files          73       73           
  Lines       14788    14788           
=======================================
  Hits        12035    12035           
  Misses       2753     2753           

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