Fix Helm Chart type error

[AdheipSingh]

Fixes #252 .

Description

---

This PR has:

• [x] been tested on a real K8S cluster to ensure creation of a brand new Druid cluster works.
• [ ] been tested for backward compatibility on a real K*S cluster by applying the changes introduced here on an existing Druid cluster. If there are any backward incompatible changes then they have been noted in the PR description.
• [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• [ ] added documentation for new or modified features or behaviors.

---

Key changed/added files in this PR

• helm
• Dockerfile

[AdheipSingh]

i will add multi-ns support in helm chart after https://github.com/druid-io/druid-operator/pull/240