update to latest circle ci builder (go 1.10.1)

[goenning]

Issue: #337

Updates to latest builder image, which uses Go 1.10.1 (this was missing from #342)

[codecov-io]

Codecov Report

Merging #343 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #343   +/-   ##
=======================================
  Coverage   72.84%   72.84%           
=======================================
  Files          71       71           
  Lines        4511     4511           
=======================================
  Hits         3286     3286           
  Misses        982      982           
  Partials      243      243

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