add codecov email notificatin.

.codecov.yml

+coverage:
+  precision: 2
+  notify:
+    email:
+      default:
+        to:
+          - sdsang@taosdata.com
+          - &author
+        only_pulls: false
+        layout: reach, diff, flags, files
+        flags: null
+        paths: null

.travis.yml

@@ -166,7 +166,7 @@ matrix:
             exit $?
           fi
 
-          bash <(curl -s https://codecov.io/bash) -f coverage.info
+          bash <(curl -s https://codecov.io/bash) -y .codecov.yml -f coverage.info
           if [ "$?" -eq "0" ]; then
             echo -e "${GREEN} ## Uploaded to Codecov! ## ${NC} "
           else