doc/encoders: fix typo in AAC encoder documentation

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

doc/encoders.texi

@@ -137,7 +137,7 @@ specifications.
 Long term prediction profile, is enabled by and will enable the aac_ltp option.
 Introduced in MPEG4.
 
-@item aac_pred
+@item aac_main
 Main-type prediction profile, is enabled by and will enable the aac_pred option.
 Introduced in MPEG2.