Pinned airshipctl v2.0 to toolbox go.mod file

Airshipctl v2.0 build was failing due to latest go.mod changes on master branch, so in the v2.0 go.mod file added reference to use v2.0 version instead of laterst version. Similar implementaion was already available other KRM functions

Closes: #619
Change-Id: Ib8290dfc0bafe720ddc039d881a91318fdc40337

krm-functions/toolbox/image/go.mod

@@ -1,8 +1,9 @@
-module opendev.org/airship/airshipctl/krm-fnunctions/toolbox/image
+module opendev.org/airship/airshipctl/krm-functions/toolbox/image
 
 go 1.14
 
 require (
+	opendev.org/airship/airshipctl v0.0.0-20210217205206-b8a4b6ad734c
 	k8s.io/api v0.17.9
 	sigs.k8s.io/kustomize/kyaml v0.10.6
 )