make ruamel.yaml requirement explicit

mr-c · mr-c · commit 0db3b1838474 · 2023-01-27T09:14:10.000+01:00
diff --git a/requirements.txt b/requirements.txt
@@ -4,3 +4,5 @@ rdflib
 requests
 CacheControl
 schema-salad >= 8.3.20220825114525, < 9
+ruamel.yaml >= 0.17.6, < 0.17.22;python_version>='3.7'
+ruamel.yaml >= 0.16.12, < 0.17.22
