squash! Update to Bones 0.5.1

This applies similar logic to removing TravisCI environments in
case tests get interrupted after making the environment but
before cleaning it up. All but the last three most recent conda
environments starting with 'travis-ci-' are removed.

.templates/hardware.sh.template

@@ -18,5 +18,10 @@
 
 {% block remote_cleanup %}
 {{ super() }}
-        conda-env remove -y -n travis-ci-$TRAVIS_JOB_NUMBER
+        # Remove all but the last three 'travis-ci-*' conda environments
+        conda-env list |
+            grep 'travis-ci-' |
+            cut -d' ' -f 1 |
+            head -n -3 |
+            xargs -I {} conda-env remove -y -n {}
 {% endblock %}