disable nightly so that Travis build passes

[zsunberg]

Removed the failing test against the nightly version of Julia from Travis - we don't support the nightly build right now

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #3   +/-   ##
=======================================
  Coverage   97.82%   97.82%           
=======================================
  Files           1        1           
  Lines          46       46           
=======================================
  Hits           45       45           
  Misses          1        1

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[coveralls]

Coverage remained the same at 97.826% when pulling 57972db on travis into 9048046 on master.