verify lfs files

tests/external/reproductions.repos.yaml

@@ -34,3 +34,8 @@
 - name: 10.5281/zenodo.1211089
   url: 10.5281/zenodo.1211089
   verify: python2 -c 'import matplotlib'
+# Test that files in git-lfs are properly cloned
+- name: LFS
+  url: https://github.com/binderhub-ci-repos/lfs
+  ref: 9abf54a
+  verify: grep "I am stored in git lfs" in-lfs.dat