Fix docker.imagePort in docs

Author: zodern

docs/docs.md

@@ -445,7 +445,7 @@ And then add a docker setup hook to login to your private registry on the server
 
 ### Image Port
 
-You can set `meteor.docker.port` to the port to expose from the container. This does not affect the port the app is accessed on, only the port the app runs on inside the docker container.
+You can set `meteor.docker.imagePort` to the port to expose from the container. This does not affect the port the app is accessed on, only the port the app runs on inside the docker container.
 
 ## Reverse Proxy