Updated upgrades.md to note quota limits changes.
Updated upgrades.md to note quota limits changes.

In particular:

  * UPDATE_QUOTA replaces the old SET_QUOTA and REMOVE_QUOTA calls.

  * Quota guarantees are still functional, but deprecated in
    preparation for optimistic offers.

Review: https://reviews.apache.org/r/71412

Gilbert88/mesos,reneploetz/mesos,dforsyth/mesos,kaysoky/mesos,dforsyth/mesos,Gilbert88/mesos,reneploetz/mesos,Gilbert88/mesos,Gilbert88/mesos,dforsyth/mesos,Gilbert88/mesos,dforsyth/mesos,abudnik/mesos,abudnik/mesos,reneploetz/mesos,kaysoky/mesos,reneploetz/mesos,dforsyth/mesos,abudnik/mesos,dforsyth/mesos,kaysoky/mesos,Gilbert88/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,dforsyth/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,kaysoky/mesos,abudnik/mesos,abudnik/mesos,kaysoky/mesos,Gilbert88/mesos,reneploetz/mesos