.gitignore: Spell Documentation in uppercase

Fixes: 4d8b843d37 ("Rename documentation -> Documentation")
Change-Id: I423cb159ca3c837ed52937dc6d76d9a43a069256
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/28634
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

.gitignore

@@ -121,12 +121,12 @@ util/autoport/autoport
 util/kbc1126/kbc1126_ec_dump
 util/kbc1126/kbc1126_ec_insert
 
-documentation/*.aux
-documentation/*.idx
-documentation/*.log
-documentation/*.toc
-documentation/*.out
-documentation/*.pdf
+Documentation/*.aux
+Documentation/*.idx
+Documentation/*.log
+Documentation/*.toc
+Documentation/*.out
+Documentation/*.pdf
 Documentation/_build
 
 doxygen/*