readme: fix "mailing list" section

Author: efiop

README.rst

@@ -164,7 +164,7 @@ details.
 Mailing List
 =========
 
-Want to stay to date? Want to help improve DVC by participating in our ocassional polls? Subscribe to our `mailing list <https://sweedom.us10.list-manage.com/subscribe/post?u=a08bf93caae4063c4e6a351f6&id=24c0ecc49a>`_. No spam, really low traffic.
+Want to stay up to date? Want to help improve DVC by participating in our ocassional polls? Subscribe to our `mailing list <https://sweedom.us10.list-manage.com/subscribe/post?u=a08bf93caae4063c4e6a351f6&id=24c0ecc49a>`_. No spam, really low traffic.
 
 Copyright
 =========