Update go.mod for go 1.16

go 1.16 is strict about go.sum changes from tests; update and tidy our
go.mod / go.sum to prevent test failures.

Author: justinsb

examples/guestbook-operator/go.mod

@@ -3,10 +3,10 @@ module sigs.k8s.io/kubebuilder-declarative-pattern/examples/guestbook-operator
 go 1.13
 
 require (
-	github.com/go-logr/logr v0.1.0
-	k8s.io/apimachinery v0.18.4
-	k8s.io/client-go v0.18.4
-	sigs.k8s.io/controller-runtime v0.6.0
+	github.com/go-logr/logr v0.3.0
+	k8s.io/apimachinery v0.20.1
+	k8s.io/client-go v0.20.1
+	sigs.k8s.io/controller-runtime v0.8.0
 	sigs.k8s.io/kubebuilder-declarative-pattern v0.0.0
 )