Documentation: standardize on url over URL

url and URL both appear in this doc. Choose url due to higher frequency

Documentation/proxy.md

@@ -27,6 +27,6 @@ etcd -proxy on -listen-client-urls 127.0.0.1:8080  -discovery https://discovery.
 ```
 
 #### Fallback to proxy mode with discovery service
-If you bootstrap a etcd cluster using [discovery service][discovery-service] with more than the expected number of etcd members, the extra etcd processes will fall back to being `readwrite` proxies by default. They will forward the requests to the cluster as described above. For example, if you create a discovery url with `size=5`, and start ten etcd processes using that same discovery URL, the result will be a cluster with five etcd members and five proxies. Note that this behaviour can be disabled with the `proxy-fallback` flag.
+If you bootstrap a etcd cluster using [discovery service][discovery-service] with more than the expected number of etcd members, the extra etcd processes will fall back to being `readwrite` proxies by default. They will forward the requests to the cluster as described above. For example, if you create a discovery url with `size=5`, and start ten etcd processes using that same discovery url, the result will be a cluster with five etcd members and five proxies. Note that this behaviour can be disabled with the `proxy-fallback` flag.
 
 [discovery-service]: https://github.com/coreos/etcd/blob/master/Documentation/clustering.md#discovery