Bug 32718: Capitalization: Display Order

Bug 32718: Capitalization: Display Order

This patch corrects the capitalization of the "Display order" column heading
in the item groups table.

To test:
0. Apply patch
1. Enable the EnableItemGroups system preference
   1.1. Go to Administration > Global system preferences
   1.2. Search for EnableItemGroups
   1.3. Change the value to "Enable"
   1.4. Click "Save all Circulation preferences"
2. Go to any bibliographic record
3. Click the "Item groups" tab at the bottom
   --> First column should be "Display order"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>