Incorrect memcache url in app.yaml

[stephenplusplus]

From @sankalpk on June 13, 2016 2:48

In appengine/express-memcached-session/app.yaml the MEMCACHE_URL is listed as localhost:11211, when it should actually be memcache:11211

Copied from original issue: googleapis/google-cloud-node#1377

[stephenplusplus]

Want to send a PR over to the nodejs-docs-samples repo? https://github.com/GoogleCloudPlatform/nodejs-docs-samples/blob/master/appengine/express-memcached-session/app.yaml