Fixes command key on Firefox MacOSx

[lbittner-pdftron]

In main.js@dispatch we are normalizing the command key to be 91 instead of FF's native 224:

if (key === 93 || key === 224) key = 91;
...

This contradicts the code in var.js that sets the command key as 224 if it's FF. We don't need this code as we are already normalizing it in the dispatch function.

[coveralls]

Pull Request Test Coverage Report for Build 187

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.9%) to 81.406%

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Totals
Change from base Build 186:	0.9%
Covered Lines:	193
Relevant Lines:	207

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💛 - Coveralls

[codecov-io]

Codecov Report

Merging #109 into master will increase coverage by 0.34%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #109      +/-   ##
==========================================
+ Coverage   92.89%   93.23%   +0.34%     
==========================================
  Files           1        1              
  Lines         211      207       -4     
==========================================
- Hits          196      193       -3     
+ Misses         15       14       -1

Impacted Files	Coverage Δ
dist/hotkeys.js	93.23% <100%> (+0.34%)	⬆️

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[jaywcjlove]

@lbittner-pdftron thx!