Merge json-2.5.1

ext/json/VERSION

@@ -1 +1 @@
-2.5.0
+2.5.1

ext/json/lib/json/common.rb

@@ -72,6 +72,8 @@ module JSON
       self.state = generator::State
       const_set :State, self.state
       const_set :SAFE_STATE_PROTOTYPE, State.new # for JRuby
+      const_set :FAST_STATE_PROTOTYPE, create_fast_state
+      const_set :PRETTY_STATE_PROTOTYPE, create_pretty_state
     ensure
       $VERBOSE = old
     end

ext/json/lib/json/version.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 module JSON
   # JSON version
-  VERSION         = '2.5.0'
+  VERSION         = '2.5.1'
   VERSION_ARRAY   = VERSION.split(/\./).map { |x| x.to_i } # :nodoc:
   VERSION_MAJOR   = VERSION_ARRAY[0] # :nodoc:
   VERSION_MINOR   = VERSION_ARRAY[1] # :nodoc: