nodeSelector unused when server.dev.enabled is true

**Describe the bug**
The helper that sets the nodeSelector for the server pods is getting skipped when the mode is set to `dev`.
https://github.com/hashicorp/vault-helm/blob/v0.13.0/templates/_helpers.tpl#L264

This causes a problem when I am attempting to experiment with vault-helm in a cluster where Linux and Windows machines reside and I want to deploy the vault server to Linux nodes only.

**To Reproduce**
Steps to reproduce the behavior:
1. Set `server.dev.enabled` to true, and define the `server.nodeSelector` setting
2. Install chart
3. Run `kubectl get pods -l app.kubernetes.io/name=vault` to get the pod name
4. Run `kubectl describe ` and note the NodeSelector isn't set

**Expected behavior**
`nodeSelector` to be used when configured even when dev is set to true

**Environment**
* Kubernetes version: 1.19
* vault-helm version: v0.13.0

Chart values:

```yaml
server:
enabled: true
dev:
enabled: true
nodeSelector: |
kubernetes.io/os: linux
```

Start at templates/_helpers.tpl around line 264 and inspect how the server pod configuration is rendered when server.dev.enabled is true. Render or install the chart with server.nodeSelector configured, then verify the resulting server pod has the expected NodeSelector while dev mode remains enabled.

Written by the indexing model from the issue text.