Remove trailing slash from host parameter in docker init.

(This causes errors on Docker 0.8)

Docker-DCO-1.1-Signed-off-by: Morgante Pell <morgante.pell@morgante.net> (github: morgante)

contrib/vagrant-docker/README.md

@@ -31,7 +31,7 @@ stop on runlevel [!2345]
 respawn
 
 script
-    /usr/bin/docker -d -H=tcp://0.0.0.0:4243/
+    /usr/bin/docker -d -H=tcp://0.0.0.0:4243
 end script
 ```