Removed obsolete ENV word

Author: rerakers

README.md

@@ -197,7 +197,7 @@ $ docker run -d -e HUB_HOST=<hub_ip|hub_name> -e REMOTE_HOST="http://node_ip|nod
 
 ### Setting Screen Resolution
 
-By default, nodes start with a screen resolution of 1360 x 1020 with a color depth of 24 bits.  These settings can be adjusted by specifying `SCREEN_WIDTH`, `SCREEN_HEIGHT` and/or `ENV SCREEN_DEPTH` environmental variables when starting the container.
+By default, nodes start with a screen resolution of 1360 x 1020 with a color depth of 24 bits.  These settings can be adjusted by specifying `SCREEN_WIDTH`, `SCREEN_HEIGHT` and/or `SCREEN_DEPTH` environmental variables when starting the container.
 
 ``` bash
 docker run -d -e SCREEN_WIDTH=1366 -e SCREEN_HEIGHT=768 -e SCREEN_DEPTH=24 selenium/standalone-firefox