Replace Sinon with simple class. Full dependency update. Bump to 3.3.4.

[Hexagon]

• Sinon is hugely overkill for what it's used for, replaced with a simple stub class (which also removes 6 sub-dependencies).
• Fix typo in readme
• Full dependency update
• Bump to 3.3.4

[codecov-commenter]

Codecov Report

Base: 92.94% // Head: 92.94% // No change to project coverage 👍

Coverage data is based on head (fb664a8) compared to base (4ab5b91).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #115   +/-   ##
=======================================
  Coverage   92.94%   92.94%           
=======================================
  Files          16       16           
  Lines        5984     5984           
=======================================
  Hits         5562     5562           
  Misses        422      422           

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[JamesCullum]

Great input as usual, thanks a lot!