Upgrade certmanager and k8s

update client-go to 1.18.8
update cert-manager to 0.15.0

Author: phiphi282

go.mod

@@ -3,14 +3,23 @@ module github.com/syseleven/designate-certmanager-webhook
 go 1.15
 
 require (
+	github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f // indirect
+	github.com/golang/groupcache v0.0.0-20191227052852-215e87163ea7 // indirect
+	github.com/google/go-cmp v0.3.1 // indirect
 	github.com/gophercloud/gophercloud v0.12.0
 	github.com/imdario/mergo v0.3.7 // indirect
-	github.com/jetstack/cert-manager v0.9.1
-	github.com/kubernetes-incubator/external-dns v0.5.15
+	github.com/jetstack/cert-manager v0.15.0
+	github.com/kubernetes-incubator/external-dns v0.5.12
+	github.com/miekg/dns v1.0.8 // indirect
 	github.com/sirupsen/logrus v1.6.0
-	k8s.io/client-go v11.0.1-0.20190409021438-1a26190bd76a+incompatible
+	golang.org/x/net v0.0.0-20191209160850-c0dbc17a3553 // indirect
+	golang.org/x/oauth2 v0.0.0-20191202225959-858c2ad4c8b6 // indirect
+	golang.org/x/sys v0.0.0-20191228213918-04cbcbbfeed8 // indirect
+	golang.org/x/time v0.0.0-20191024005414-555d28b269f0 // indirect
+	google.golang.org/appengine v1.6.5 // indirect
+	google.golang.org/genproto v0.0.0-20191230161307-f3c370f40bfb // indirect
+	k8s.io/client-go v0.18.8
+	k8s.io/utils v0.0.0-20200729134348-d5654de09c73 // indirect
 )
 
-replace k8s.io/client-go => k8s.io/client-go v0.19.1
-
 replace git.apache.org/thrift.git => github.com/apache/thrift v0.13.0