Bump required Go version to 1.15

[corneliusweig]

No description provided.

[codecov-commenter]

Codecov Report

Merging #86 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #86   +/-   ##
=======================================
  Coverage   52.40%   52.40%           
=======================================
  Files           8        8           
  Lines         250      250           
=======================================
  Hits          131      131           
  Misses         97       97           
  Partials       22       22           

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