travis: update go versions

[dvrkps]

No description provided.

[codecov]

Codecov Report

Merging #633 into master will decrease coverage by 0.57%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #633      +/-   ##
==========================================
- Coverage    78.3%   77.72%   -0.58%     
==========================================
  Files         130      130              
  Lines       10231    10231              
==========================================
- Hits         8011     7952      -59     
- Misses       1358     1430      +72     
+ Partials      862      849      -13

Impacted Files	Coverage Δ
plumbing/transport/ssh/common.go	20.54% <0%> (-45.21%)	⬇️
plumbing/transport/ssh/auth_method.go	31.57% <0%> (-22.81%)	⬇️

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