.gitlab-ci.yml: Bump tags for testsuite images

These new images come with pinned versions of `pytest` and `pylint`:

- `pylint`: `== 2.1.1`
- `pytest`: `>= 3.7`

.gitlab-ci.yml

-image: buildstream/testsuite-debian:9-master-112-a9f63c5e
+image: buildstream/testsuite-debian:9-master-114-4cab18e3
 
 cache:
   key: "$CI_JOB_NAME-"
@@ -79,25 +79,25 @@ source_dist:
     - coverage-linux/
 
 tests-debian-9:
-  image: buildstream/testsuite-debian:9-master-112-a9f63c5e
+  image: buildstream/testsuite-debian:9-master-114-4cab18e3
   <<: *linux-tests
 
 tests-fedora-27:
-  image: buildstream/testsuite-fedora:27-master-112-a9f63c5e
+  image: buildstream/testsuite-fedora:27-master-114-4cab18e3
   <<: *linux-tests
 
 tests-fedora-28:
-  image: buildstream/testsuite-fedora:28-master-112-a9f63c5e
+  image: buildstream/testsuite-fedora:28-master-114-4cab18e3
   <<: *linux-tests
 
 tests-ubuntu-18.04:
-  image: buildstream/testsuite-ubuntu:18.04-master-112-a9f63c5e
+  image: buildstream/testsuite-ubuntu:18.04-master-114-4cab18e3
   <<: *linux-tests
 
 tests-unix:
   # Use fedora here, to a) run a test on fedora and b) ensure that we
   # can get rid of ostree - this is not possible with debian-8
-  image: buildstream/testsuite-fedora:27-master-112-a9f63c5e
+  image: buildstream/testsuite-fedora:27-master-114-4cab18e3
   stage: test
   variables:
     BST_FORCE_BACKEND: "unix"