Fix Jenkins tests

Dockerfile.jenkins

@@ -1,5 +1,4 @@
 FROM schemers/chibi:head
 RUN apt-get update && apt-get install -y \
     gcc ca-certificates libffi-dev docker.io make
-ARG timestamp=0
-RUN snow-chibi install --impls=chibi --always-yes retropikzel.test-r7rs && echo "${timestamp}"
+RUN snow-chibi install --impls=chibi --always-yes retropikzel.test-r7rs

Jenkinsfile

@@ -3,8 +3,7 @@ pipeline {
         dockerfile {
             label 'docker-x86_64'
             filename 'Dockerfile.jenkins'
-            args '--user=root --privileged -v /var/run/docker.sock:/var/run/docker.sock'
-            additionalBuildArgs "--build-arg timestamp=${currentBuild.startTimeInMillis}"
+            args '-t --user=root --privileged -v /var/run/docker.sock:/var/run/docker.sock'
             reuseNode true
         }
     }