chore(deps): update teslamate/grafana docker tag to v3.1.0

[renovate]

This PR contains the following updates:

Package	Update	Change
teslamate/grafana	minor	3.0.0 → 3.1.0

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Release Notes

grafana/grafana (teslamate/grafana)

v3.1.0: Grafana v3.1.0

For full details read the Grafana 3.1 Release blog post.

Download
Installation

Release Highlights

• Dashboard Repository at Grafana.net. You can now discover and upload dashboards.
• Dashboard time range and variables values are now always synced with URL.
• Constant Template Variable have been added to make dashboard sharing easier (use as metric prefix).
• Singlestat can now map ranges to text.
• Metrics Grafana now supports sending metrics about itself.
• Full changelog

Breaking changes

• Logging format have been changed to improve log filtering.
• Graphite PNG Graphite PNG support dropped from Graph panel (use Grafana native PNG instead).
• Migration No longer possible to migrate dashboards from 1.x (Stored in ES or Influx 0.8).

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