Docs: add ApiVersion to /version for remote API 1.12

Docker-DCO-1.1-Signed-off-by: Paul Morie <pmorie@gmail.com> (github: pmorie)

docs/sources/reference/api/docker_remote_api_v1.12.md

@@ -1164,6 +1164,7 @@ Show the docker version information
         Content-Type: application/json
 
         {
+             "ApiVersion":"1.12",
              "Version":"0.2.2",
              "GitCommit":"5a2a5cc+CHANGES",
              "GoVersion":"go1.0.3"