Enable errorlint Linter

[tri-adam]

Enable errorlint linter, which finds code that will cause problems with the error wrapping scheme introduced in Go 1.13. Fix related lint.

[codecov-commenter]

Codecov Report

Merging #160 (a6d8c41) into master (55a90f0) will not change coverage.
The diff coverage is 40.00%.

@@           Coverage Diff           @@
##           master     #160   +/-   ##
=======================================
  Coverage   75.13%   75.13%           
=======================================
  Files          28       28           
  Lines        2441     2441           
=======================================
  Hits         1834     1834           
  Misses        466      466           
  Partials      141      141           

Impacted Files	Coverage Δ
pkg/integrity/metadata.go	58.51% <0.00%> (ø)
pkg/integrity/select.go	68.22% <50.00%> (ø)
pkg/sif/descriptor_input.go	84.41% <50.00%> (ø)
pkg/integrity/verify.go	78.90% <100.00%> (ø)

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