[fr] correction backported from 3.0
'Themed' should be 'Theme'

Looks like a small typo there. While using assets from `app/webroot` the folder name should be `theme` instead of `themed`.

Tested on ver. 2.5.4 and 2.5.5. for JS files.
Merge pull request #1853 from ankitpokhrel/patch-1

'themed' should be 'theme'
[fr][ja] Follow #1853