update go mod to 1.15

Author: phiphi282

go.mod

@@ -1,6 +1,6 @@
 module github.com/syseleven/designate-certmanager-webhook
 
-go 1.12
+go 1.15
 
 require (
 	github.com/gophercloud/gophercloud v0.12.0

go.sum

@@ -105,6 +105,8 @@ github.com/emicklei/go-restful v2.9.3+incompatible/go.mod h1:otzb+WCGbkyDHkqmQmT
 github.com/envoyproxy/go-control-plane v0.6.9/go.mod h1:SBwIajubJHhxtWwsL9s8ss4safvEdbitLhGGK48rN6g=
 github.com/evanphx/json-patch v0.0.0-20190203023257-5858425f7550 h1:mV9jbLoSW/8m4VK16ZkHTozJa8sesK5u5kTMFysTYac=
 github.com/evanphx/json-patch v0.0.0-20190203023257-5858425f7550/go.mod h1:50XU6AFN0ol/bzJsmQLiYLvXMP4fmwYFNcr97nuDLSk=
+github.com/evanphx/json-patch v4.5.0+incompatible h1:ouOWdg56aJriqS0huScTkVXPC5IcNrDCXZ6OoTAWu7M=
+github.com/evanphx/json-patch v4.5.0+incompatible/go.mod h1:50XU6AFN0ol/bzJsmQLiYLvXMP4fmwYFNcr97nuDLSk=
 github.com/exoscale/egoscale v0.11.0/go.mod h1:Ee3U4ZjSDpbbEc9VkQ/jttUU8USE8Nv7L3YzVi03Y1U=
 github.com/fatih/structs v1.1.0/go.mod h1:9NiDSp5zOcgEDl+j00MP/WkGVPOlPRLejGD8Ga6PJ7M=
 github.com/ffledgling/pdns-go v0.0.0-20180219074714-524e7daccd99/go.mod h1:4mP9w9+vYGw2jUx2+2v03IA+phyQQjNRR4AL3uxlNrs=