Enable docs update. (#78)

Just forget to add deploy_key to this repository.

paddle/scripts/travis/docs.sh

@@ -59,8 +59,5 @@ chmod 600 deploy_key
 eval `ssh-agent -s`
 ssh-add deploy_key
 
-# Temporarily disable automatic doc deployment due to permission issue.
-exit 0
-
 # Push
 git push $SSH_REPO $TARGET_BRANCH