[BUGFIX] Use correct font awesome icon for text file type

Use the correct class "fa-file-text".

Resolves: #62322
Releases: master
Change-Id: I2ebc743aad88b3fcb91152f27f20d48c0258c044
Reviewed-on: http://review.typo3.org/33384
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>