Bump github.com/moby/buildkit from 0.18.0 to 0.18.1

Bumps [github.com/moby/buildkit](https://github.com/moby/buildkit) from 0.18.0 to 0.18.1.
- [Release notes](https://github.com/moby/buildkit/releases)
- [Commits](moby/buildkit@v0.18.0...v0.18.1)

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

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

go.mod

@@ -53,7 +53,7 @@ require (
 	github.com/mattn/go-zglob v0.0.6
 	github.com/mgutz/ansi v0.0.0-20200706080929-d51e80ef957d
 	github.com/miekg/dns v1.1.62
-	github.com/moby/buildkit v0.18.0
+	github.com/moby/buildkit v0.18.1
 	github.com/moby/patternmatcher v0.6.0
 	github.com/morikuni/aec v1.0.0
 	github.com/muesli/termenv v0.15.2

go.sum

@@ -461,8 +461,8 @@ github.com/mitchellh/ioprogress v0.0.0-20180201004757-6a23b12fa88e h1:Qa6dnn8Dla
 github.com/mitchellh/ioprogress v0.0.0-20180201004757-6a23b12fa88e/go.mod h1:waEya8ee1Ro/lgxpVhkJI4BVASzkm3UZqkx/cFJiYHM=
 github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
-github.com/moby/buildkit v0.18.0 h1:KSelhNINJcNA3FCWBbGCytvicjP+kjU5kZlZhkTUkVo=
-github.com/moby/buildkit v0.18.0/go.mod h1:vCR5CX8NGsPTthTg681+9kdmfvkvqJBXEv71GZe5msU=
+github.com/moby/buildkit v0.18.1 h1:Iwrz2F/Za2Gjkpwu3aM2LX92AFfJCJe2oNnvGNvh2Rc=
+github.com/moby/buildkit v0.18.1/go.mod h1:vCR5CX8NGsPTthTg681+9kdmfvkvqJBXEv71GZe5msU=
 github.com/moby/docker-image-spec v1.3.1 h1:jMKff3w6PgbfSa69GfNg+zN/XLhfXJGnEx3Nl2EsFP0=
 github.com/moby/docker-image-spec v1.3.1/go.mod h1:eKmb5VW8vQEh/BAr2yvVNvuiJuY6UIocYsFu/DxxRpo=
 github.com/moby/locker v1.0.1 h1:fOXqR41zeveg4fFODix+1Ch4mj/gT0NE1XJbp/epuBg=