update to csi-test v3.0.0

v3.0.0 fixed "go mod" support by adding the /v3 suffix to import paths
(kubernetes-csi/csi-test#232). dep currently
does not support that
(golang/dep#1962 (comment)) and
can only import that with symlink workarounds in csi-test and by
disabling pruning.

Author: pohly

Gopkg.lock

@@ -24,6 +24,10 @@
   go-tests = true
   unused-packages = true
 
+  [[prune.project]]
+    name = "github.com/kubernetes-csi/csi-test"
+    unused-packages = false
+
 [[constraint]]
   name = "github.com/container-storage-interface/spec"
   version = "1.0.0"
@@ -42,7 +46,8 @@
 
 [[constraint]]
   name = "github.com/kubernetes-csi/csi-test"
-  version = "2.1.0"
+  source = "github.com/pohly/csi-test"
+  branch = "fix-semver"
 
 # We have to select the right version by name because of the "kubernetes-" prefix, dep doesn't
 # recognize these as normal releases. Upstream is considering to change the tagging,