Update to python3.8

Our base CI image doesn't have python3.7 anymore so bump this up to
running on 3.8.

Change-Id: Ifa13fe62247bedd77771628aace15ad47e86e07c

.zuul.yaml

@@ -56,12 +56,12 @@
     check:
       jobs:
         - tox-pep8
-        - tox-py37
+        - tox-py38
         - gerritbot-build-opendev-image
     gate:
       jobs:
         - tox-pep8
-        - tox-py37
+        - tox-py38
         - gerritbot-upload-opendev-image
     promote:
       jobs:

Dockerfile

@@ -13,12 +13,12 @@
 # You should have received a copy of the GNU General Public License
 # along with this software.  If not, see <http://www.gnu.org/licenses/>.
 
-FROM opendevorg/python-builder:3.7 as builder
+FROM opendevorg/python-builder:3.8 as builder
 
 COPY . /tmp/src
 RUN assemble
 
-FROM opendevorg/python-base:3.7 as gerritbot
+FROM opendevorg/python-base:3.8 as gerritbot
 
 COPY --from=builder /output/ /output
 RUN /output/install-from-bindep

setup.cfg

@@ -13,7 +13,7 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [entry_points]
 console_scripts =

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py37,pep8
+envlist = py38,pep8
 
 [testenv]
 usedevelop = True