Fix test

Author: mattn

test/test_heredoc.ok

@@ -1,2 +1,3 @@
-(let =<< a (heredoc (list ) "EOS" (list "hello" " world")))
+(let =<< a (heredoc (list) "EOS" (list "hello" " world")))
 (let =<< a (heredoc (list "trim") "EOS" (list "\thello" "world")))
+(let =<< a (heredoc (list) "EOS" (list)))

test/test_heredoc.vim

@@ -6,3 +6,5 @@ let a =<< trim EOS
 	hello
 world
 EOS
+let a =<< EOS
+EOS