dropped python3.5 testing, adding python3.8

2.7, i'm looking at you.

.gitlab-ci.yml

@@ -83,10 +83,6 @@ test:python2.7:
   <<: *test
   image: python:2.7
 
-test:python3.5:
-  <<: *test
-  image: python:3.5
-
 test:python3.6:
   <<: *test
   image: python:3.6
@@ -95,6 +91,10 @@ test:python3.7:
   <<: *test
   image: python:3.7
 
+test:python3.8:
+  <<: *test
+  image: python:3.8
+
 # -- test -------------------
 .integration: &integration_test
   stage: integration
@@ -122,10 +122,6 @@ integration:python2.7:
   <<: *integration_test
   image: python:2.7
 
-integration:python3.5:
-  <<: *integration_test
-  image: python:3.5
-
 integration:python3.6:
   <<: *integration_test
   image: python:3.6
@@ -134,6 +130,10 @@ integration:python3.7:
   <<: *integration_test
   image: python:3.7
 
+integration:python3.8:
+  <<: *integration_test
+  image: python:3.8
+
 # -- docs -------------------
 # Although we don't host the docs on Gitlab Pages,
 # we still want to check that they build properly.