Bump golang.org/x/tools from 0.1.12 to 0.4.0 (#99)

Bumps [golang.org/x/tools](https://github.com/golang/tools) from 0.1.12 to 0.4.0.
- [Release notes](https://github.com/golang/tools/releases)
- [Commits](https://github.com/golang/tools/compare/v0.1.12...v0.4.0)

---
updated-dependencies:
- dependency-name: golang.org/x/tools
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -11,6 +11,6 @@ require (
 	github.com/tj/assert v0.0.3
 	github.com/ulikunitz/xz v0.5.10
 	github.com/xor-gate/ar v0.0.0-20170530204233-5c72ae81e2b7
-	golang.org/x/tools v0.1.12
+	golang.org/x/tools v0.4.0
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 )