Use the more generic "gnome-open" to edit a file rather than "gedit". This is a very simple, one-line fix that can provide the ability to use an alternate editor in the short term until a formal configuration solution is implemented.

sed -i 's/gedit/gnome-open/' shell/src/main/java/org/jboss/forge/shell/plugins/builtin/EditPlugin.java

You may want to take it one step further and check if gnome-open is there. If not, try kde-open. As a last resort, you can just open the file normally (like the view plugin).