Bump github.com/guregu/null

Bumps [github.com/guregu/null](https://github.com/guregu/null) from 3.4.0+incompatible to 3.5.0+incompatible.
- [Release notes](https://github.com/guregu/null/releases)
- [Commits](https://github.com/guregu/null/compare/v3.4.0...v3.5.0)

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

go.mod

@@ -14,7 +14,7 @@ require (
 	github.com/gorilla/mux v1.7.4
 	github.com/gorilla/schema v1.0.2
 	github.com/gorilla/sessions v1.2.0
-	github.com/guregu/null v3.4.0+incompatible
+	github.com/guregu/null v3.5.0+incompatible
 	github.com/hashicorp/go-multierror v1.0.0
 	github.com/ikeikeikeike/go-sitemap-generator/v2 v2.0.2
 	github.com/jteeuwen/go-bindata v3.0.7+incompatible // indirect

go.sum

@@ -67,6 +67,8 @@ github.com/gorilla/sessions v1.2.0 h1:S7P+1Hm5V/AT9cjEcUD5uDaQSX0OE577aCXgoaKpYb
 github.com/gorilla/sessions v1.2.0/go.mod h1:dk2InVEVJ0sfLlnXv9EAgkf6ecYs/i80K/zI+bUmuGM=
 github.com/guregu/null v3.4.0+incompatible h1:a4mw37gBO7ypcBlTJeZGuMpSxxFTV9qFfFKgWxQSGaM=
 github.com/guregu/null v3.4.0+incompatible/go.mod h1:ePGpQaN9cw0tj45IR5E5ehMvsFlLlQZAkkOXZurJ3NM=
+github.com/guregu/null v3.5.0+incompatible h1:fSdvRTQtmBA4B4YDZXhLtxTIJZYuUxBFTTHS4B9djG4=
+github.com/guregu/null v3.5.0+incompatible/go.mod h1:ePGpQaN9cw0tj45IR5E5ehMvsFlLlQZAkkOXZurJ3NM=
 github.com/hashicorp/errwrap v1.0.0 h1:hLrqtEDnRye3+sgx6z4qVLNuviH3MR5aQ0ykNJa/UYA=
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-multierror v1.0.0 h1:iVjPR7a6H0tWELX5NxNe7bYopibicUzc7uPribsnS6o=