Bump github.com/gorilla/mux from 1.8.0 to 1.8.1

Bumps [github.com/gorilla/mux](https://github.com/gorilla/mux) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/gorilla/mux/releases)
- [Commits](gorilla/mux@v1.8.0...v1.8.1)

---
updated-dependencies:
- dependency-name: github.com/gorilla/mux
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

go.mod

@@ -5,7 +5,7 @@ go 1.14
 require (
 	github.com/go-git/go-git/v5 v5.9.0
 	github.com/google/go-github/v32 v32.1.0
-	github.com/gorilla/mux v1.8.0
+	github.com/gorilla/mux v1.8.1
 	github.com/markbates/pkger v0.17.1
 	github.com/mitchellh/ioprogress v0.0.0-20180201004757-6a23b12fa88e
 	github.com/pkg/errors v0.9.1