Textile reader: skip over attribute in image source.

We don't have a place yet for styles or sizes on images, but
we can skip the attributes rather than incorrectly taking them
to be part of the filename.

Closes #2515.

src/Text/Pandoc/Readers/Textile.hs

@@ -535,6 +535,7 @@ link = try $ do
 image :: Parser [Char] ParserState Inlines
 image = try $ do
   char '!' >> notFollowedBy space
+  _ <- attributes -- ignore for now, until we have image attributes
   src <- manyTill anyChar' (lookAhead $ oneOf "!(")
   alt <- option "" (try $ (char '(' >> manyTill anyChar' (char ')')))
   char '!'