release_notes: fix version

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/RELEASE_NOTES

@@ -12,7 +12,7 @@ This release enables frame-based multithreaded decoding for a number of codecs,
 including theora, huffyuv, VP8, H.263, mpeg4 and H.264. Additionally, there has
 been a major cleanup of
 both internal and external APIs. For this reason, the major versions of all
-libraries have been bumped. On the one hand, this means that 0.7 can be installed
+libraries have been bumped. On the one hand, this means that 0.8 can be installed
 side-by-side with previous releases, on the other hand, in order to benefit
 from the new features, applications need to be recompiled.