change quotation mark to backtick (#123)

I previously erroneously used quotation marks.

Author: Wout van Heeswijk

README.md

@@ -32,7 +32,7 @@ All variables which can be overridden are stored in [defaults/main.yml](defaults
 | `grafana_data_dir` | /var/lib/grafana | Path to database directory |
 | `grafana_address` | 0.0.0.0 | Address on which grafana listens |
 | `grafana_port` | 3000 | port on which grafana listens |
-| 'grafana_cap_net_bind_service' | false | Enables the use of ports below 1024 without root privilages by leveraging the 'capabilities' of the linux kernel. read: http://man7.org/linux/man-pages/man7/capabilities.7.html |
+| `grafana_cap_net_bind_service` | false | Enables the use of ports below 1024 without root privilages by leveraging the 'capabilities' of the linux kernel. read: http://man7.org/linux/man-pages/man7/capabilities.7.html |
 | `grafana_url` | "http://{{ grafana_address }}:{{ grafana_port }}" | Full URL used to access Grafana from a web browser |
 | `grafana_api_url` | "{{ grafana_url }}" | URL used for API calls in provisioning if different from public URL. See [this issue](https://github.com/cloudalchemy/ansible-grafana/issues/70). |
 | `grafana_domain` | "{{ ansible_fqdn \| default(ansible_host) \| default('localhost') }}" | setting is only used in as a part of the `root_url` option. Useful when using GitHub or Google OAuth |