fixup! [infra] Validate pull requests in TaskCluster

.taskcluster.yml

@@ -55,7 +55,7 @@ tasks:
                 owner: ${event.pusher.email}
                 source: ${event.repository.url}
               payload:
-                image: gsnedders/web-platform-tests:0.13
+                image: jugglinmike/web-platform-tests:0.18
                 maxRunTime: 7200
                 artifacts:
                   public/results:
@@ -120,7 +120,7 @@ tasks:
               owner: ${event.pull_request.user.login}@users.noreply.github.com
               source: ${event.repository.url}
             payload:
-              image: gsnedders/web-platform-tests:0.13
+              image: jugglinmike/web-platform-tests:0.18
               maxRunTime: 7200
               artifacts:
                 $if: operation.creates_artifacts

tools/docker/Dockerfile

@@ -69,4 +69,10 @@ WORKDIR /home/test/
 
 COPY .bashrc /home/test/.bashrc
 
+# Ubuntu inserts a logout script which exits with a non-zero status. This makes
+# it impossible to use the `exit` built-in from a login shell where the `-e`
+# option has been set. Since the script is intended to clear the console for
+# interactive sessions, it may safely be removed.
+RUN rm /home/test/.bash_logout
+
 COPY start.sh /home/test/start.sh