Fixed typo "video of audio" to "video or audio"

Author: kke

source/applications/gridfs.txt

@@ -20,7 +20,7 @@ When you query a GridFS store for a file, the driver or client will
 reassemble the chunks as needed. You can perform range queries on
 files stored through GridFS.  You also can access information from
 arbitrate sections of files, which allows you to "skip" into the
-middle of a video of audio file.
+middle of a video or audio file.
 
 GridFS is useful not only for storing files that exceed 16MB but also
 for storing any files for which you want access without having to load