fix insert call

repo2docker/buildpacks/repo2docker-entrypoint

@@ -28,7 +28,7 @@ def main():
     # base locations
     log_dirs = [".", tempfile.gettempdir()]
     if "REPO_DIR" in os.environ:
-        log_dirs.insert(os.environ["REPO_DIR"], 0)
+        log_dirs.insert(0, os.environ["REPO_DIR"])
     for d in log_dirs:
         log_path = join(d, 'log.txt')
         try: