Bump api version to 1.21.

Signed-off-by: David Calavera <david.calavera@gmail.com>

api/common.go

@@ -17,7 +17,7 @@ import (
 // Common constants for daemon and client.
 const (
 	// Current REST API version
-	Version version.Version = "1.20"
+	Version version.Version = "1.21"
 
 	// Minimun REST API version supported
 	MinVersion version.Version = "1.12"

docs/reference/api/docker_remote_api.md

@@ -36,13 +36,13 @@ parent = "smn_remoteapi"
    Client applications need to take this into account to ensure
    they will not break when talking to newer Docker daemons.
 
-The current version of the API is v1.20
+The current version of the API is v1.21
 
 Calling `/info` is the same as calling
-`/v1.20/info`.
+`/v1.21/info`.
 
 You can still call an old version of the API using
-`/v1.19/info`.
+`/v1.20/info`.
 
 ## Docker Events
 
@@ -60,6 +60,12 @@ Running `docker rmi` emits an **untag** event when removing an image name.  The
 
 > **Acknowledgement**: This diagram and the accompanying text were used with the permission of Matt Good and Gilder Labs. See Matt's original blog post [Docker Events Explained](http://gliderlabs.com/blog/2015/04/14/docker-events-explained/).
 
+## v1.21
+
+### Full documentation
+
+[*Docker Remote API v1.21*](/reference/api/docker_remote_api_v1.21/)
+
 ## v1.20
 
 ### Full documentation