use 4.x so that 4.0.0.beta2 is included

Author: rmosolgo

lib/react/jsx/sprockets_strategy.rb

@@ -23,7 +23,7 @@ def attach_with_strategy(sprockets_env, strategy_or_nil)
       # @return [Symbol] based on the environment, return a method name to call with the sprockets environment
       def detect_strategy
         sprockets_version = Gem::Version.new(Sprockets::VERSION)
-        if sprockets_version >= Gem::Version.new("4.0.0")
+        if sprockets_version >= Gem::Version.new("4.x")
           :register_processors
         elsif sprockets_version >= Gem::Version.new("3.0.0")
           :register_engine_with_mime_type