Remove auto-load for `Hashie.logger`

The auto-load is never triggered because there is no `Hashie::Logger`
constant to trigger it. We need to `require` the file in the top level
`hashie.rb` and anywhere else that uses it (in case someone just loads a
single file).

At the moment, this is only used in Mash, so we're covered.

lib/hashie.rb

@@ -1,8 +1,7 @@
-require 'logger'
+require 'hashie/logger'
 require 'hashie/version'
 
 module Hashie
-  autoload :Logger,             'hashie/logger'
   autoload :Clash,              'hashie/clash'
   autoload :Dash,               'hashie/dash'
   autoload :Hash,               'hashie/hash'

lib/hashie/logger.rb

@@ -1,3 +1,5 @@
+require 'logger'
+
 module Hashie
   # The logger that Hashie uses for reporting errors.
   #