To do this you need to execute this script:
OutlinerWindow; dockControl -area "left"-content outlinerPanel1-label "outliner"-allowedArea "left"-allowedArea "right"-width 250;deleteUI "outlinerPanel1Window" ;
To run this script you open:
(Maya) Window > General Editors > Script Editor
Copy and paste the script and press PLAY (triangle) and that is all.
Here how it looks