Ignore the locally generated SSSOM files.

The cl-local mapping set only depends on the -edit file, so it can
always be re-generated from a fresh copy of the repository without
needing to download external resources -- therefore there's no need to
commit it to the repository.

Likewise for the "meta" set.

.gitignore

@@ -59,6 +59,8 @@ src/ontology/subsets/BDS_subset.tsv
 src/ontology/subsets/BDS_subset.owl
 src/ontology/subsets/BDS_subset.obo
 src/ontology/subsets/BDS_subset.json
+src/mappings/cl-local.sssom.tsv
+src/mappings/cl.sssom.tsv
 cl.json
 cl.owl
 cl-simple.owl