Use hash comparison to check for LE certs
Use hash comparison to check for LE certs

Fixes #65.

Instead of checking where a symlink points to, compare the hashes of the
TLS certificate installed for an app and the TLS certificate marked as
'current' by let's encrypt to determine whether the app is currently
secured by the plugin.

sseemayer/dokku-letsencrypt,dokku/dokku-letsencrypt