Specify version for mockgen package

[mickmister]

Summary

See #213 (comment)

[codecov-commenter]

Codecov Report

Merging #232 (94e035f) into master (9411708) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #232   +/-   ##
=======================================
  Coverage   23.80%   23.80%           
=======================================
  Files          62       62           
  Lines        2541     2541           
=======================================
  Hits          605      605           
  Misses       1857     1857           
  Partials       79       79           

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[mickmister]

@hanzei The linter is complaining and saying that go mod tidy needs to be run. When I run go mod tidy, the original error returns:

go install github.com/golang/mock/mockgen
../../../../pkg/mod/github.com/golang/[email protected]/mockgen/parse.go:35:2: missing go.sum entry for module providing package golang.org/x/tools/go/packages (imported by github.com/golang/mock/mockgen); to add:
        go get github.com/golang/mock/[email protected]
make: *** [mock] Error 1

I'm not sure what needs to be done here

[hanzei]

Let's skip QA review as this is only a build tooling change.