docs: remove wrong entry in modules

Author: mdelapenya

mkdocs.yml

@@ -85,7 +85,6 @@ nav:
         - modules/dynamodb.md
         - modules/elasticsearch.md
         - modules/etcd.md
-        - modules/firebase.md
         - modules/gcloud.md
         - modules/grafana-lgtm.md
         - modules/inbucket.md