KeepAlive should be a number.

According to these docs:
http://mongodb.github.io/node-mongodb-native/driver-articles/mongoclient.html#server-a-hash-of-options-at-the-server-level-not-supported-by-the-url
http://nodejs.org/api/net.html#net_socket_setkeepalive_enable_initialdelay
KeepAlive should be a number.