Fix git review -d M,N with later gerrit
Fix git review -d M,N with later gerrit

It seems the "number" field returned via gerrit JSON can be a string
(2.13) or a integer (~2.14).  Ensure we can handle both.

Change-Id: I3cbda6c07343332aba592bd96fd8545f08a2cbfe

openstack-infra/git-review