Make the replica transformer kind aware.

The previous implementation had a bug and poorly handled
types that should not have a `spec: replica:` field.

Documentation is updated to reflect the change in behavior,
and better highlights the cases where a patch should be
used instead of this shorthand.

docs/fields.md

@@ -355,6 +355,7 @@ Replicas modified the number of replicas for a resource.
 E.g. Given this kubernetes Deployment fragment:
 
 ```
+kind: Deployment
 metadata:
   name: deployment-name
 spec:
@@ -374,6 +375,17 @@ This field accepts a list, so many resources can
 be modified at the same time.
 
 
+#### Limitation
+As this declaration does not take in a `kind:` nor a `group:`
+it will match any `group` and `kind` that has a matching name and
+that is one of:
+- `Deployment`
+- `ReplicationController`
+- `ReplicaSet`
+- `StatefulSet`
+
+For more complex use cases, revert to using a patch.
+
 
 ### resources