Add usedforsecurity flag to md5 hashing

[jandrej]

This PR adds the usedforsecurity flag to the md5 hash call. On FIPS enabled machines the plain command leads to an error.

I don't know the behavior on non-FIPS machines. The flag might not be available so there might be need for guarding the call.

[codecov[bot]]

Codecov Report

Merging #177 (7ad5e62) into master (c0e399b) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #177   +/-   ##
=======================================
  Coverage   85.99%   86.00%           
=======================================
  Files          11       11           
  Lines        4427     4430    +3     
=======================================
+ Hits         3807     3810    +3     
  Misses        620      620           

Impacted Files	Coverage Δ
fortls/parse_fortran.py	88.34% <100.00%> (+0.02%)	:arrow_up:

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