Added linux open-folder keybind.

Moved application:open-dev to `ctrl-alt-o`

keymaps/linux.cson

@@ -10,7 +10,8 @@
   'ctrl-shift-i': 'window:toggle-dev-tools'
   'ctrl-alt-p': 'window:run-package-specs'
   'ctrl-alt-s': 'application:run-all-specs'
-  'ctrl-shift-o': 'application:open-dev'
+  'ctrl-alt-o': 'application:open-dev'
+  'ctrl-shift-o': 'application:open-folder'
   'F11': 'window:toggle-full-screen'
 
   # Sublime Parity