Fixed YAML metadata with "chomp" (|-).

Previously if a YAML block under `|-` contained
a blank line, pandoc would not parse it as metadata.

src/Text/Pandoc/Readers/Markdown.hs

@@ -290,8 +290,8 @@ toMetaValue :: PandocMonad m
 toMetaValue x =
   parseFromString' parser' (T.unpack x)
   where parser' = (asInlines <$> ((trimInlinesF . mconcat)
-                       <$> (guard (not endsWithNewline)
-                             *> manyTill inline eof)))
+                       <$> try (guard (not endsWithNewline)
+                                *> manyTill inline eof)))
                   <|> (asBlocks <$> parseBlocks)
         asBlocks p = do
           p' <- p

test/command/yaml-with-chomp.md

@@ -0,0 +1,12 @@
+```
+% pandoc -s -t native
+---
+ml: |-
+    TEST
+
+    BLOCK
+...
+^D
+Pandoc (Meta {unMeta = fromList [("ml",MetaBlocks [Para [Str "TEST"],Plain [Str "BLOCK"]])]})
+[]
+```