fixup! Reuse Rack::Utils#build_nested_query

Author: jdufresne

lib/rack/test/utils.rb

@@ -6,7 +6,7 @@ module Utils # :nodoc:
       include Rack::Utils
       extend self
 
-      if Rack.release < '3.1.0'
+      if Gem::Version.new(Rack.release) < Gem::Version.new("3.1")
         # Build a query string for the given value and prefix. The value
         # can be an array or hash of parameters.
         def build_nested_query(value, prefix = nil)