Fix flake8 errors

Signed-off-by: Ulysses Souza <ulyssessouza@gmail.com>

compose/cli/main.py

@@ -1080,7 +1080,7 @@ class TopLevelCommand(object):
                 log.error(
                     "The image for the service you're trying to recreate has been removed. "
                     "If you continue, volume data could be lost. Consider backing up your data "
-                    "before continuing.\n".format(e.explanation)
+                    "before continuing.\n"
                 )
                 res = yesno("Continue with the new image? [yN]", False)
                 if res is None or not res:

compose/service.py

@@ -1157,7 +1157,7 @@ class Service(object):
         container_name = build_container_name(
             self.project, service_name, number, slug,
         )
-        ext_links_origins = [l.split(':')[0] for l in self.options.get('external_links', [])]
+        ext_links_origins = [link.split(':')[0] for link in self.options.get('external_links', [])]
         if container_name in ext_links_origins:
             raise DependencyError(
                 'Service {0} has a self-referential external link: {1}'.format(