Tag for 0.6.4

[Govinda-Fichtner]

Hello, could you please also create a tag for consul:0.6.4 on the Docker Hub?

$ docker pull gliderlabs/consul:0.6.4
Pulling repository docker.io/gliderlabs/consul
Tag 0.6.4 not found in repository docker.io/gliderlabs/consul

It seems currently there is only a latest tag available:

$ docker run -ti gliderlabs/consul --version
Consul v0.6.4
Consul Protocol: 3 (Understands back to: 1)

By the ways thanks for your awesome work!