recipetool: add missed module

When I use recipetool to add a new recipe, it says:

[snip]
sys.exit(14)
NameError: name 'sys' is not defined
[snip]

(From OE-Core rev: 051e1c27bbf6a5898f2cf13b78dd3d8d1ec31586)

Signed-off-by: Lei Yang <Lei.Yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/recipetool/create_npm.py

@@ -16,6 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
 import os
+import sys
 import logging
 import subprocess
 import tempfile