Deploy only if php == '7.1'

[montymxb]

Current deployment for latest master runs a gh-pages deploy for every version of php we are running against. This clarifies it should only run for 7.1.

[codecov]

Codecov Report

Merging #337 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #337   +/-   ##
=======================================
  Coverage   98.79%   98.79%           
=======================================
  Files          35       35           
  Lines        2749     2749           
=======================================
  Hits         2716     2716           
  Misses         33       33

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