[2.0.0-5]+ A `meta` tag is added even if only `header` is requested as delivery method

I updated ` ember-cli-content-security-policy` from `2.0.0-4` to `2.0.0` and my HTML validator warned me of the following - `Potentially bad value for attribute “content” on XHTML element “meta”: Invalid base64-value (should be multiple of 4 bytes: 7).`. No idea what that error means but it lead me to finding that since upgrading a `meta` tag with my CSP settings has appeared. My settings contain `delivery: ['header']`. The same happens when I try `2.0.0-5`. Downgrading to `2.0.0-4` fixes the issue.

cc @jelhan