FEATURE: upgrade sprockets to latest stable

This unlocks Rails upgrades, so we can now upgrade to latest Rails

lib/es6_module_transpiler/sprockets.rb

@@ -1,3 +1,4 @@
 require 'sprockets'
 
-Sprockets.register_engine '.es6', Tilt::ES6ModuleTranspilerTemplate
+Sprockets.register_mime_type 'application/ecmascript6', extensions: ['.es6', '.js.es6'], charset: :unicode
+Sprockets.register_transformer 'application/ecmascript6', 'application/javascript', Tilt::ES6ModuleTranspilerTemplate

lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb

@@ -10,6 +10,15 @@ module Tilt
     @mutex = Mutex.new
     @ctx_init = Mutex.new
 
+    def self.call(input)
+      filename = input[:filename]
+      source = input[:data]
+      context = input[:environment].context_class.new(input)
+
+      result = new(filename){source}.render(context)
+      context.metadata.merge(data: result)
+    end
+
     def prepare
       # intentionally left empty
       # Tilt requires this method to be defined