Fix typo in documentation.

doc/org.texi

@@ -890,7 +890,7 @@ of a headline), then a headline like the current one will be inserted
 after the end of the subtree.
 @kindex C-@key{RET}
 @item C-@key{RET}
-Just like @kbd{M-@key{RET}, but if the heading is inserted after the current,
+Just like @kbd{M-@key{RET}}, but if the heading is inserted after the current,
 insert it actually after the entire subtree.
 @kindex M-S-@key{RET}
 @item M-S-@key{RET}