update URL in gemspec

GitHub now redirects all user pages to the github.io domain. Switch to
this newer domain name.

GitHub pages have HTTPS available. Switch to the HTTPS encrypted
version.

docile.gemspec

@@ -6,7 +6,7 @@ Gem::Specification.new do |s|
   s.version     = Docile::VERSION
   s.authors     = ['Marc Siegel']
   s.email       = %w(msiegel@usainnov.com)
-  s.homepage    = 'http://ms-ati.github.com/docile/'
+  s.homepage    = 'https://ms-ati.github.io/docile/'
   s.summary     = 'Docile keeps your Ruby DSLs tame and well-behaved'
   s.description = 'Docile turns any Ruby object into a DSL. Especially useful with the Builder pattern.'
   s.license     = 'MIT'