work around ansible 2.5 'become' breakage

I can't find anything in the release notes, but Ansible 2.5 changed
*something* with playbooks running as root and 'become'ing a regular user to
copy files. Pasting the error here for other poor bastards googling:

failed: [lobsters.xen.prgmr.com] (item={'file': 'ssh/known_hosts', 'mode': '0600'}) => {"item": {"file": "ssh/known_hosts", "mode": "0600"}, "msg": "Authentication or permission failure. In some cases, you may have been able to authenticate and did not have permissions on the target directory. Consider changing the remote tmp path in ansible.cfg to a path rooted in \"/tmp\". Failed command was: ( umask 77 && mkdir -p \"` echo ~None/.ansible/tmp/ansible-tmp-1527081889.4756002-145395363159875 `\" && echo ansible-tmp-1527081889.4756002-145395363159875=\"` echo ~None/.ansible/tmp/ansible-tmp-1527081889.4756002-145395363159875 `\" ), exited with result 1", "unreachable": true}

ansible.cfg

@@ -2,6 +2,7 @@
 inventory = ./inventories/prod.ini
 log_path = ./lobsters-ansible.log
 callback_whitelist = profile_tasks
+remote_tmp = /tmp/ansible
 
 [ssh_connection]
 ssh_args = -C -o ControlMaster=auto -o ControlPersist=60s -o PreferredAuthentications=publickey