windows: Fix an oops in a test causing AppVeyor to fail.
@@ -357,7 +357,7 @@ class TestBadImport < TestCase
# Don't check preloaded packages for slashed paths.
var message = """\
- SyntaxError: Cannot import 'abc/def':\n \
+ SyntaxError: Cannot import 'abc\/def':\n \
from [test]:1:\n\
"""
