parse_decimal(): Parse spaces as group separators if the group separator is nbsp

[akx]

Fixes #637

[codecov-io]

Codecov Report

Merging #649 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #649      +/-   ##
==========================================
+ Coverage   90.98%   90.98%   +<.01%     
==========================================
  Files          24       24              
  Lines        4171     4173       +2     
==========================================
+ Hits         3795     3797       +2     
  Misses        376      376

Impacted Files	Coverage Δ
babel/numbers.py	97.68% <100%> (+0.01%)	⬆️

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