LaTeX reader: Fixed parsing of paragraphs beginning with a group.

Previously a paragraph beginning ``` {``}hello{''} ``` would be
parsed as two paragraphs.

Closes #606.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -203,8 +203,8 @@ block = (mempty <$ comment)
     <|> environment
     <|> mempty <$ macro -- TODO improve macros, make them work everywhere
     <|> blockCommand
-    <|> grouped block
     <|> paragraph
+    <|> grouped block
     <|> (mempty <$ char '&')  -- loose & in table environment