Restrict to older eslint rules.

- Restricted to older version to avoid needing a newer eslint.
- This will be updated once older Node.js support is dropped and a newer
  eslint can be used.

Author: davidlehn

package.json

@@ -56,7 +56,7 @@
     "cors": "^2.7.1",
     "cross-env": "^5.2.0",
     "eslint": "^6.8.0",
-    "eslint-config-digitalbazaar": "^2.3.0",
+    "eslint-config-digitalbazaar": "2.5.x",
     "express": "^4.16.4",
     "fs-extra": "^8.1.0",
     "join-path-js": "0.0.0",