Node 0.12 compatibility

[sushruth]

At least with --harmony flag

[codecov]

Codecov Report

Merging #62 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #62   +/-   ##
=======================================
  Coverage   98.88%   98.88%           
=======================================
  Files           1        1           
  Lines          90       90           
  Branches       17       17           
=======================================
  Hits           89       89           
  Misses          1        1

Impacted Files	Coverage Δ
lib/index.js	98.88% <100%> (ø)	✅

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