Fixed FluentNumber parsing crashing on non-US locales

[Mailaender]

Closes https://github.com/blushingpenguin/Fluent.Net/issues/11

[codecov[bot]]

Codecov Report

Merging #12 (fd4980d) into master (6624035) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #12   +/-   ##
=======================================
  Coverage   93.79%   93.79%           
=======================================
  Files          26       26           
  Lines        1886     1887    +1     
=======================================
+ Hits         1769     1770    +1     
  Misses        117      117           

Impacted Files	Coverage Δ
Fluent.Net/MessageContext.cs	94.24% <100.00%> (+0.04%)	:arrow_up:

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