PubSub 'ackDeadline' cannot be configured when creating a subscription

[lc-chrisbarton]

See https://github.com/GoogleCloudPlatform/google-cloud-node/blob/pubsub-0.14.0/packages/pubsub/src/subscription.js

ackDeadline is hardcoded to 'this.ackDeadline = 10000;' where-as maxConnections can be configured 'this.maxConnections = options.maxConnections || 5;'