Add `murmurhash-js` to deps

[bstream]

Hi 👋

Since you are using murmurhash-js in src (https://github.com/nathanmarks/jss-theme-reactor/blob/master/src/styleManager.js#L3) it should be a dependency.

[codecov[bot]]

Codecov Report

Merging #40 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #40   +/-   ##
=======================================
  Coverage   94.11%   94.11%           
=======================================
  Files           4        4           
  Lines         119      119           
=======================================
  Hits          112      112           
  Misses          7        7

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[nathanmarks]

Oops... danke!