update helm dependency to 2.7.2

Author: databus23

glide.lock

@@ -1,18 +1,17 @@
 package: github.com/sapcc/kubernikus
-testImport:
+import:
 - package: github.com/stretchr/testify
   version: ^1.1.0
   subpackages:
   - assert
-import:
 - package: github.com/spf13/cobra
   subpackages:
   - cobra
 - package: k8s.io/client-go
   version: release-4.0
 - package: github.com/kennygrant/sanitize
 - package: k8s.io/helm
-  version: v2.5.0
+  version: v2.7.2
 - package: k8s.io/apiextensions-apiserver
   version: release-1.7
 - package: k8s.io/code-generator