Convenience: resetVersion config in chartpress.yaml

This allows usage of `chartpress --reset` to restore Chart.yaml and
values.yaml to what it was before using `chartpress`. It can be useful
to avoid committing unrelated changes to Chart.yaml and values.yaml
after local development.

pangeo/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: pangeo
-version: AUTO_POPULATED_BY_CHARTPRESS_AND_TRAVIS
+version: 0.0.1-set.by.chartpress
 description: An extention of jupyterhub with extra Pangeo resources
 maintainers:
   - name: Jacob Tomlinson (Met Office)