Use VERSION file instead of hard-coded value

Author: hsbt

json_pure.gemspec

@@ -2,7 +2,7 @@
 
 Gem::Specification.new do |s|
   s.name = "json_pure".freeze
-  s.version = "2.3.0"
+  s.version = File.read("VERSION").chomp
 
   s.required_rubygems_version = Gem::Requirement.new(">= 0".freeze) if s.respond_to? :required_rubygems_version=
   s.require_paths = ["lib".freeze]