Fix tarfile mode parameter that doesn't work in 3.4
@@ -352,7 +352,7 @@ class BuildPack(LoggingConfigurable):
def build(self, image_spec):
tarf = io.BytesIO()
- tar = tarfile.open(fileobj=tarf, mode='x')
+ tar = tarfile.open(fileobj=tarf, mode='w')
dockerfile_tarinfo = tarfile.TarInfo("Dockerfile")
dockerfile = self.render().encode('utf-8')
dockerfile_tarinfo.size = len(dockerfile)
