gem: fix license name to standard, explicitly set required ruby version

.travis.yml

@@ -1,3 +1,4 @@
+sudo: false
 language: ruby
 rvm:
   - 2.5

README.md

@@ -1,6 +1,6 @@
 # dyndnsd.rb
 
-[![Build Status](https://travis-ci.org/cmur2/dyndnsd.png)](https://travis-ci.org/cmur2/dyndnsd)
+[![Build Status](https://travis-ci.org/cmur2/dyndnsd.svg?branch=dyndnsd-2.x)](https://travis-ci.org/cmur2/dyndnsd) [![Dependencies](https://badges.depfu.com/badges/4f25da8493f7a29f652ac892fbf9227b/overview.svg)](https://depfu.com/github/cmur2/dyndnsd)
 
 A small, lightweight and extensible DynDNS server written with Ruby and Rack.
 

dyndnsd.gemspec

@@ -10,16 +10,16 @@ Gem::Specification.new do |s|
   s.description = 'A small, lightweight and extensible DynDNS server written with Ruby and Rack.'
   s.author  = 'Christian Nicolai'
   s.email = 'chrnicolai@gmail.com'
-  s.license = 'Apache License Version 2.0'
   s.homepage  = 'https://github.com/cmur2/dyndnsd'
+  s.license = 'Apache-2.0'
 
   s.files = `git ls-files`.split($/)
   s.test_files = s.files.grep(%r{^(test|spec|features)/})
-
   s.require_paths = ['lib']
-
   s.executables = ['dyndnsd']
 
+  s.required_ruby_version = '>= 2.3'
+
   s.add_runtime_dependency 'rack', '~> 2.0'
   s.add_runtime_dependency 'json'
   s.add_runtime_dependency 'metriks'