add docker server version to /info

Signed-off-by: Zhang Kun <zkazure@gmail.com>

docs/reference/api/docker_remote_api.md

@@ -88,6 +88,7 @@ This section lists each version from latest to oldest.  Each listing includes a
 list of DNS options to be used in the container.
 * `POST /build` now optionally takes a serialized map of build-time variables.
 * `GET /events` now includes a `timenano` field, in addition to the existing `time` field.
+* `GET /info` now lists engine version information.
 
 ### v1.20 API changes
 

docs/reference/api/docker_remote_api_v1.21.md

@@ -1860,6 +1860,7 @@ Display system-wide information
         },
         "SwapLimit": false,
         "SystemTime": "2015-03-10T11:11:23.730591467-07:00"
+        "ServerVersion": "1.9.0"
     }
 
 Status Codes:

docs/reference/commandline/info.md

@@ -21,6 +21,7 @@ For example:
     $ docker -D info
     Containers: 14
     Images: 52
+    Engine Version: 1.9.0
     Storage Driver: aufs
      Root Dir: /var/lib/docker/aufs
      Backing Filesystem: extfs