encoding-example-profiles: fix "oac" typo

Fixes issue mpv-player#10.

Author: divVerent

etc/encoding-example-profiles.conf

@@ -81,8 +81,8 @@ ovcopts = qscale=4
 
 [enc-v-vp8]
 profile-desc = "VP8 (libvpx)"
-oac = libvpx
-oacopts = qmin=4,b=10000000k # ought to be enough for anyone; for CBR use, set b=; for VBR use, set qmin= to quality
+ovc = libvpx
+ovcopts = qmin=4,b=10000000k # ought to be enough for anyone; for CBR use, set b=; for VBR use, set qmin= to quality
 
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 # formats #