Update copyright year in NOTICE

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

NOTICE

@@ -1,5 +1,5 @@
 Docker
-Copyright 2012-2014 Docker, Inc.
+Copyright 2012-2015 Docker, Inc.
 
 This product includes software developed at Docker, Inc. (http://www.docker.com).