update constraint for oslo.cache to new release 2.1.0

Change-Id: I0b0191e57d9dd4fe144128e1c683d307098fe144
meta:version: 2.1.0
meta:diff-start: -
meta:series: ussuri
meta:release-type: release
meta:pypi: yes
meta:first: no
meta:release:Author: Ben Nemec <bnemec@redhat.com>
meta:release:Commit: Ben Nemec <bnemec@redhat.com>
meta:release:Change-Id: I8ff829a8884688d23d3c8298b3c09eb484148e28
meta:release:Code-Review+2: Hervé Beraud <hberaud@redhat.com>
meta:release:Code-Review+2: Sean McGinnis <sean.mcginnis@gmail.com>
meta:release:Workflow+1: Sean McGinnis <sean.mcginnis@gmail.com>

upper-constraints.txt

@@ -508,8 +508,8 @@ sushy===3.1.0
 python-neutronclient===7.1.0
 pika===1.1.0
 oslo.cache===1.38.1;python_version=='2.7'
-oslo.cache===2.0.0;python_version=='3.6'
-oslo.cache===2.0.0;python_version=='3.7'
+oslo.cache===2.1.0;python_version=='3.6'
+oslo.cache===2.1.0;python_version=='3.7'
 WebTest===2.0.34
 openstack.nose-plugin===0.11
 os-collect-config===11.0.0