doc/APIchanges: Fix bistream typo

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/APIchanges

@@ -22,7 +22,7 @@ API changes, most recent first:
 
 2016-xx-xx - xxxxxxx - lavc 57.15.0 - avcodec.h
   Add a new bitstream filtering API working with AVPackets.
-  Deprecate the old bistream filtering API.
+  Deprecate the old bitsream filtering API.
 
 2016-xx-xx - xxxxxxx - lavfi 6.42.0 - avfilter.h
   Add AVFilterContext.hw_device_ctx.