kured: remove extra quotes from annotation

Remove extra quotes from annotation kured lock annotation. Before this
patch, the annotation created would look like:

```
weave.works/kured-node-lock: '''{"nodeID":"manual"}'''
```

With this patch, the annotation looks like:

```
weave.works/kured-node-lock: '{"nodeID":"manual"}'
```

(cherry picked from commit 4403054)

internal/pkg/skuba/kured/kured.go

@@ -27,7 +27,7 @@ import (
 
 const (
 	kuredDSName             = "kured"
-	kuredLockAnnotationJson = `{"metadata":{"annotations":{"weave.works/kured-node-lock":"'{\"nodeID\":\"manual\"}'"}}}`
+	kuredLockAnnotationJson = `{"metadata":{"annotations":{"weave.works/kured-node-lock":"{\"nodeID\":\"manual\"}"}}}`
 )
 
 func LockExists(client clientset.Interface) (bool, error) {