Use absolute paths for internal autoloads

So that we don't need to rely on the LOAD_PATH.

Author: deivid-rodriguez

lib/thor/base.rb

@@ -8,9 +8,9 @@
 require_relative "util"
 
 class Thor
-  autoload :Actions,    "thor/actions"
-  autoload :RakeCompat, "thor/rake_compat"
-  autoload :Group,      "thor/group"
+  autoload :Actions,    File.expand_path("actions", __dir__)
+  autoload :RakeCompat, File.expand_path("rake_compat", __dir__)
+  autoload :Group,      File.expand_path("group", __dir__)
 
   # Shortcuts for help.
   HELP_MAPPINGS       = %w(-h -? --help -D)

lib/thor/shell.rb

@@ -24,9 +24,9 @@ module Shell
     SHELL_DELEGATED_METHODS = [:ask, :error, :set_color, :yes?, :no?, :say, :say_status, :print_in_columns, :print_table, :print_wrapped, :file_collision, :terminal_width]
     attr_writer :shell
 
-    autoload :Basic, "thor/shell/basic"
-    autoload :Color, "thor/shell/color"
-    autoload :HTML,  "thor/shell/html"
+    autoload :Basic, File.expand_path("shell/basic", __dir__)
+    autoload :Color, File.expand_path("shell/color", __dir__)
+    autoload :HTML,  File.expand_path("shell/html", __dir__)
 
     # Add shell to initialize config values.
     #