test-import: use printf instead of echo

tests/test-import.t

@@ -440,9 +440,8 Test fuzziness (ambiguous patch location
 
 import with --no-commit should have written .hg/last-message.txt
 
-  $ echo '\n' | cat .hg/last-message.txt -
+  $ printf '\n' | cat .hg/last-message.txt -
   change
-  
 
 
 test fuzziness with eol=auto