provisioners/docker: fix linux cap for daemon running

CHANGELOG.md

@@ -3,6 +3,8 @@
 BUG FIXES:
 
   - command/rsync-auto: Works properly on Windows.
+  - guests/linux: Fix test for Docker provisioner whether Docker is
+      running.
 
 ## 1.5.3 (April 14, 2014)
 

plugins/provisioners/docker/cap/linux/docker_daemon_running.rb

@@ -4,7 +4,7 @@ module VagrantPlugins
       module Linux
         module DockerDaemonRunning
           def self.docker_daemon_running(machine)
-            machine.communicate.test("test -f /var/run/docker/pid")
+            machine.communicate.test("test -f /var/run/docker.pid")
           end
         end
       end