Map generation: Strict check on SUBDOMAIN_INSTALL fails

[ChrisHardie]

The commit f29005c introduced a strict comparison for the check that the Multisite setup is using a SUBDOMAIN_INSTALL at https://github.com/rtCamp/nginx-helper/blob/master/admin/class-nginx-helper-admin.php#L502.

Unfortunately while the non-strict check against yes was succeeding in the past when SUBDOMAIN_INSTALL is true, the strict check does not, taking the map generation into the subdirectory code path. This produces unexpected results, including an invalid "path" value where a domain value is expected in the map entry for any site that doesn't have a domain mapped.