Bump sigs.k8s.io/controller-runtime from 0.6.4 to 0.8.3

Bumps [sigs.k8s.io/controller-runtime](https://github.com/kubernetes-sigs/controller-runtime) from 0.6.4 to 0.8.3.
- [Release notes](https://github.com/kubernetes-sigs/controller-runtime/releases)
- [Commits](kubernetes-sigs/controller-runtime@v0.6.4...v0.8.3)

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

go.mod

@@ -14,15 +14,14 @@ require (
 	github.com/giantswarm/ruleengine v0.2.0
 	github.com/giantswarm/to v0.3.0
 	github.com/prometheus/client_golang v1.9.0
-	github.com/stretchr/testify v1.6.1 // indirect
 	golang.org/x/tools v0.0.0-20200706234117-b22de6825cf7 // indirect
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6
-	k8s.io/api v0.18.9
-	k8s.io/apiextensions-apiserver v0.18.9
-	k8s.io/apimachinery v0.18.9
-	k8s.io/client-go v0.18.9
+	k8s.io/api v0.20.2
+	k8s.io/apiextensions-apiserver v0.20.1
+	k8s.io/apimachinery v0.20.2
+	k8s.io/client-go v0.20.2
 	sigs.k8s.io/cluster-api v0.3.13
-	sigs.k8s.io/controller-runtime v0.6.4
+	sigs.k8s.io/controller-runtime v0.8.3
 )
 
 replace sigs.k8s.io/cluster-api v0.3.13 => github.com/giantswarm/cluster-api v0.3.10-gs