mention OL file location

Author: jmckenna

en/cgi/openlayers.txt

@@ -104,7 +104,7 @@ Customizing settings
 Location of the embedded OpenLayers.js file
 -------------------------------------------
 
-If you aren't providing your own OpenLayers library through `MS_OPENLAYERS_JS_UR`, 
+If you aren't providing your own OpenLayers library through `MS_OPENLAYERS_JS_URL`, 
 MapServer will point to a hardcoded filepath of `www.mapserver.org/lib` to find the OpenLayers 
 library, referred to in [maptemplate.c](https://github.com/MapServer/MapServer/blob/main/src/maptemplate.c#L54).