Update Json file

Why
* There's a security warning for the json gem < 2.3.0

How
* Update the gemlock and the gemfile to install json gem >= 2.3.0

Gemfile.lock

@@ -16,7 +16,7 @@ GEM
       tins (~> 1.6)
     diff-lcs (1.3)
     docile (1.3.1)
-    json (2.1.0)
+    json (2.3.1)
     rake (13.0.1)
     redis (4.1.1)
     rspec (3.5.0)
@@ -48,6 +48,7 @@ PLATFORMS
 DEPENDENCIES
   connection_pool (~> 2.2)
   coveralls (~> 0.8)
+  json (~> 2.3.1, >= 2.3.0)
   rake (~> 13.0, >= 11.1.2)
   redlock!
   rspec (~> 3, >= 3.0.0)

redlock.gemspec

@@ -1,27 +1,29 @@
-# coding: utf-8
-lib = File.expand_path('../lib', __FILE__)
+# frozen_string_literal: true
+
+lib = File.expand_path('lib', __dir__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'redlock/version'
 
 Gem::Specification.new do |spec|
-  spec.name          = "redlock"
+  spec.name          = 'redlock'
   spec.version       = Redlock::VERSION
-  spec.authors       = ["Leandro Moreira"]
-  spec.email         = ["leandro.ribeiro.moreira@gmail.com"]
-  spec.summary       = %q{Distributed lock using Redis written in Ruby.}
-  spec.description   = %q{Distributed lock using Redis written in Ruby. Highly inspired by https://github.com/antirez/redlock-rb.}
-  spec.homepage      = "https://github.com/leandromoreira/redlock-rb"
+  spec.authors       = ['Leandro Moreira']
+  spec.email         = ['leandro.ribeiro.moreira@gmail.com']
+  spec.summary       = 'Distributed lock using Redis written in Ruby.'
+  spec.description   = 'Distributed lock using Redis written in Ruby. Highly inspired by https://github.com/antirez/redlock-rb.'
+  spec.homepage      = 'https://github.com/leandromoreira/redlock-rb'
   spec.license       = 'BSD-2-Clause'
 
   spec.files         = `git ls-files -z`.split("\x0")
   spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
-  spec.require_paths = ["lib"]
+  spec.require_paths = ['lib']
 
   spec.add_dependency 'redis', '>= 3.0.0', '< 5.0'
 
-  spec.add_development_dependency "coveralls", "~> 0.8"
+  spec.add_development_dependency 'connection_pool', '~> 2.2'
+  spec.add_development_dependency 'coveralls', '~> 0.8'
+  spec.add_development_dependency 'json', '>= 2.3.0', '~> 2.3.1'
   spec.add_development_dependency 'rake', '>= 11.1.2', '~> 13.0'
   spec.add_development_dependency 'rspec', '~> 3', '>= 3.0.0'
-  spec.add_development_dependency 'connection_pool', '~> 2.2'
 end