bump version to 1.13.0-rc6

Signed-off-by: Victor Vieux <vieux@docker.com>

CHANGELOG.md

@@ -5,7 +5,7 @@ information on the list of deprecated flags and APIs please have a look at
 https://docs.docker.com/engine/deprecated/ where target removal dates can also
 be found.
 
-## 1.13.0 (2017-01-10)
+## 1.13.0 (2017-01-18)
 
 **IMPORTANT**: In Docker 1.13, the managed plugin api changed, as compared to the experimental
 version introduced in Docker 1.12. You must **uninstall** plugins which you installed with Docker 1.12

VERSION

@@ -1 +1 @@
-1.13.0-rc5
+1.13.0-rc6