Avoid 'is False'

[tovrstra]

The old code goes against PEP8. See https://www.python.org/dev/peps/pep-0008/ (Look for Don't compare boolean values to True or False) A similar issue in pdb.py is being fixed in PR #250.

[codecov]

Codecov Report

Merging #251 (a80dc95) into master (4a9b322) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #251   +/-   ##
=======================================
  Coverage   95.56%   95.56%           
=======================================
  Files          74       74           
  Lines        8048     8048           
  Branches     1040     1040           
=======================================
  Hits         7691     7691           
  Misses        169      169           
  Partials      188      188           

Impacted Files	Coverage Δ
iodata/formats/mol2.py	89.71% <100.00%> (ø)

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