replaced numpy.NAN,INF with numpy.nan,inf

[orbeckst]

fix #290

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 0.00%. Comparing base (a5bcc8a) to head (ab88637).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
gromacs/fileformats/xvg.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #292   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         22      22           
  Lines       3954    3954           
=====================================
  Misses      3954    3954           

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