Fix typo in units python script

[albfan]

@k-takata I found this problem trying the new vala parser.

I guess is related with a buggy implementation as vala parser actually SIGSEV.

[codecov-io]

Codecov Report

Merging #2326 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2326   +/-   ##
=======================================
  Coverage   86.23%   86.23%           
=======================================
  Files         176      176           
  Lines       35712    35712           
=======================================
  Hits        30797    30797           
  Misses       4915     4915

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[coveralls]

Coverage remained the same at 86.355% when pulling 6ab7d72 on albfan:shrink-typo into 496721d on universal-ctags:master.

[masatake]

@albfan, thank you!

[k-takata]

Thank you for finding this.