Added concurrency support to the cucumber formatter

[lonnblad]

#256

[codecov]

Codecov Report

Merging #273 into master will increase coverage by 0.09%.
The diff coverage is 96.11%.

@@            Coverage Diff             @@
##           master     #273      +/-   ##
==========================================
+ Coverage   84.83%   84.92%   +0.09%     
==========================================
  Files          16       16              
  Lines        2526     2528       +2     
==========================================
+ Hits         2143     2147       +4     
+ Misses        264      262       -2     
  Partials      119      119              

Impacted Files	Coverage Δ
suite.go	88.18% <ø> (ø)
fmt_cucumber.go	92.50% <96.00%> (+0.06%)	⬆️
fmt.go	94.57% <100.00%> (+0.02%)	⬆️
run.go	80.26% <100.00%> (+1.31%)	⬆️

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