Bump acme-client to version 2.0.15

Update unixcharles/acme-client from 2.0.14 to 2.0.15

Changelog: changed

Author: dependencies.io Bot

config/software/acme-client.rb

@@ -15,7 +15,7 @@
 #
 
 name 'acme-client'
-default_version '2.0.14'
+default_version '2.0.15'
 
 license 'MIT'
 license_file 'LICENSE.txt'