Fixed doc markup that was causing RDoc to ignore part of the README

README.rdoc

@@ -152,7 +152,7 @@ are called before and after the processing of each attachment), and the
 attachment-specific "before_<attachment>_post_process" and
 "after_<attachment>_post_process". The callbacks are intended to be as close to
 normal ActiveRecord callbacks as possible, so if you return false (specifically
--- returning nil is not the same) in a before_ filter, the post processing step
+- returning nil is not the same) in a before_ filter, the post processing step
 will halt. Returning false in an after_ filter will not halt anything, but you
 can access the model and the attachment if necessary.