remove node 4.2 from test matrix (superceded by v4)

[aoberoi]

Should fix test failure in #90

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #91 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   95.41%   95.41%           
=======================================
  Files           4        4           
  Lines         131      131           
=======================================
  Hits          125      125           
  Misses          6        6

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