Cosmetics: Typo

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17757 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/APIchanges

 20090301 - r17682 - lavf 52.31.0 - Generic metadata API
-  This version introduce a new metadata API (see av_metadata_get() and friends).
+  This version introduces a new metadata API (see av_metadata_get() and friends).
   The old API is now deprecated and shouldn't be used anymore. This especially
   include the following structure fields:
     - AVFormatContext.title