Fix - Support IE 11

[nicksrandall]

See: https://developer.mozilla.org/en-US/docs/Web/API/Window/crypto

[codecov-commenter]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master        #3   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           30        31    +1     
=========================================
+ Hits            30        31    +1     

Impacted Files	Coverage Δ
src/browser.js	100.00% <100.00%> (ø)

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