planning: update index.json to in-progress

Author: cowwoc

.cat/issues/v2/v2.1/build-git-filter-repo-ci/index.json

@@ -1,5 +1,6 @@
 {
-  "status": "open",
-  "dependencies": [],
-  "blocks": ["2.1-replace-bfg-with-git-filter-repo"]
-}
+  "status" : "in-progress",
+  "dependencies" : [ ],
+  "blocks" : [ "2.1-replace-bfg-with-git-filter-repo" ],
+  "targetBranch" : "v2.1"
+}