Bump github.com/jetstack/cert-manager from 1.5.4 to 1.6.0 (#365)

Bumps [github.com/jetstack/cert-manager](https://github.com/jetstack/cert-manager) from 1.5.4 to 1.6.0.
- [Release notes](https://github.com/jetstack/cert-manager/releases)
- [Commits](cert-manager/cert-manager@v1.5.4...v1.6.0)

---
updated-dependencies:
- dependency-name: github.com/jetstack/cert-manager
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

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

go.mod

@@ -1,7 +1,7 @@
 module github.com/Shopify/kubeaudit
 
 require (
-	github.com/jetstack/cert-manager v1.5.4
+	github.com/jetstack/cert-manager v1.6.0
 	github.com/sirupsen/logrus v1.8.1
 	github.com/spf13/cobra v1.2.1
 	github.com/stretchr/testify v1.7.0