Make unclejack the official Vagrantfile maintainer

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

MAINTAINERS

@@ -6,4 +6,4 @@ Michael Crosby <michael@crosbymichael.com> (@crosbymichael)
 api.go: Victor Vieux <victor@dotcloud.com> (@vieux)
 Dockerfile: Tianon Gravi <admwiggin@gmail.com> (@tianon)
 Makefile: Tianon Gravi <admwiggin@gmail.com> (@tianon)
-Vagrantfile: Daniel Mizyrycki <daniel@dotcloud.com> (@mzdaniel)
+Vagrantfile: Cristian Staretu <cristian.staretu@gmail.com> (@unclejack)