Escape parameter on generated response

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | NA

If a template with an `<esi>` tag  is configured with an URL containing a `'` (in  `src` or `alt`) ; the HttpCache will generate invalide php code.

It's not a security issue, given the template and the `<esi>` tag is written by the developper, but, as the character quote is allowed in URL (https://tools.ietf.org/html/rfc3986) it coud be a potential bug.