chore(commitlintrc): change "footer-max-line-length" to warn

Don't throw a commitlint error for:

```
footer's lines must not be longer than 100 characters
```

.commitlintrc.json

@@ -2,6 +2,7 @@
   "extends": ["@commitlint/config-conventional"],
   "rules": {
     "body-max-line-length": [1, "always", 100],
+    "footer-max-line-length": [1, "always", 100],
     "type-empty": [2, "never"]
   }
 }