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](https://github.com/gorilla/mux/compare/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>

go.mod

@@ -16,7 +16,7 @@ require (
 	github.com/gopherjs/gopherjs v0.0.0-20181103185306-d547d1d9531e // indirect
 	github.com/gorilla/csrf v1.7.1
 	github.com/gorilla/feeds v1.1.1
-	github.com/gorilla/mux v1.8.0
+	github.com/gorilla/mux v1.8.1
 	github.com/gorilla/schema v1.2.0
 	github.com/gorilla/sessions v1.2.1
 	github.com/guregu/null v4.0.0+incompatible

go.sum

@@ -80,8 +80,8 @@ github.com/gorilla/css v1.0.0/go.mod h1:Dn721qIggHpt4+EFCcTLTU/vk5ySda2ReITrtgBl
 github.com/gorilla/feeds v1.1.1 h1:HwKXxqzcRNg9to+BbvJog4+f3s/xzvtZXICcQGutYfY=
 github.com/gorilla/feeds v1.1.1/go.mod h1:Nk0jZrvPFZX1OBe5NPiddPw7CfwF6Q9eqzaBbaightA=
 github.com/gorilla/mux v1.7.4/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
-github.com/gorilla/mux v1.8.0 h1:i40aqfkR1h2SlN9hojwV5ZA91wcXFOvkdNIeFDP5koI=
-github.com/gorilla/mux v1.8.0/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
+github.com/gorilla/mux v1.8.1 h1:TuBL49tXwgrFYWhqrNgrUNEY92u81SPhu7sTdzQEiWY=
+github.com/gorilla/mux v1.8.1/go.mod h1:AKf9I4AEqPTmMytcMc0KkNouC66V3BtZ4qD5fmWSiMQ=
 github.com/gorilla/schema v1.2.0 h1:YufUaxZYCKGFuAq3c96BOhjgd5nmXiOY9NGzF247Tsc=
 github.com/gorilla/schema v1.2.0/go.mod h1:kgLaKoK1FELgZqMAVxx/5cbj0kT+57qxUrAlIO2eleU=
 github.com/gorilla/securecookie v1.1.1 h1:miw7JPhV+b/lAHSXz4qd/nN9jRiAFV5FwjeKyCS8BvQ=