Remove double quotes from copyright message

Needed because we transclude the copyright message into a head meta
tag. IE11 was complaining; other browsers didn’t seem to mind.

core/copyright.tid

@@ -21,7 +21,7 @@ modification, are permitted provided that the following conditions are met:
   contributors may be used to endorse or promote products derived from
   this software without specific prior written permission.
 
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 'AS IS'
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE