CI: Drop py35, add py38, move to gtk3

.gitlab-ci.yml

@@ -157,27 +157,27 @@ variables:
     - bash ./.ci/test_template.sh
 
 
-test:3.5:
+test:3.6:
   stage: test
-  image: pauldmccarthy/fsleyes-py35-wxpy4-gtk2
+  image: pauldmccarthy/fsleyes-py36-wxpy4-gtk3
   <<: *test_template
 
 
-test:3.6:
+test:3.7:
   stage: test
-  image: pauldmccarthy/fsleyes-py36-wxpy4-gtk2
+  image: pauldmccarthy/fsleyes-py37-wxpy4-gtk3
   <<: *test_template
 
 
-test:3.7:
+test:3.8:
   stage: test
-  image: pauldmccarthy/fsleyes-py37-wxpy4-gtk2
+  image: pauldmccarthy/fsleyes-py38-wxpy4-gtk3
   <<: *test_template
 
 
 test:build-pypi-dist:
   stage: test
-  image: pauldmccarthy/fsleyes-py35-wxpy4-gtk2
+  image: pauldmccarthy/fsleyes-py36-wxpy4-gtk3
   <<: *except_releases
 
   tags:
@@ -195,7 +195,7 @@ test:build-pypi-dist:
 
 style:
   stage: style
-  image: pauldmccarthy/fsleyes-py35-wxpy4-gtk2
+  image: pauldmccarthy/fsleyes-py36-wxpy4-gtk3
   <<: *test_template
   variables:
     TEST_STYLE:  "true"