Tell users to enable module mode in go env #11

[MatthewCroughan]

fixes #11

[codecov-commenter]

Codecov Report

Merging #12 into master will decrease coverage by 2.39%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #12      +/-   ##
==========================================
- Coverage   92.82%   90.42%   -2.40%     
==========================================
  Files          19       19              
  Lines         794      794              
==========================================
- Hits          737      718      -19     
- Misses         33       54      +21     
+ Partials       24       22       -2     

Impacted Files	Coverage Δ
cmd_selfupdate.go	17.85% <0.00%> (-67.86%)	⬇️

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