udpate navigation (#74)

Author: QiJune

_data/navigation.yml

@@ -4,6 +4,6 @@ main:
   - title: "Documents"
     url: doc_index/sqlflow
   - title: "ElasticDL"
-    url: "https://sql-machine-learning.github.io/elasticdl"
+    url: "https://elasticdl.github.io"
   - title: "GitHub"
     url: https://github.com/sql-machine-learning