bump dependencies

Author: stefan-as

.rubocop.yml

@@ -1,3 +1,6 @@
+AllCops:
+  TargetRubyVersion: 2.3
+
 Style/FrozenStringLiteralComment:
   Enabled: false
 

quayio-scanner.gemspec

@@ -12,15 +12,17 @@ Gem::Specification.new do |spec|
   spec.homepage      = 'https://github.com/aboutsource/quayio-scanner'
   spec.license       = 'MIT'
 
+  spec.required_ruby_version = '>= 2.3.0'
+
   spec.files = `git ls-files -z`.split("\x0").reject do |f|
     f.match(%r{^(test|spec|features)/})
   end
   spec.executables   = Dir.glob('bin/**/*.rb').map { |file| File.basename(file) }
   spec.require_paths = ['lib']
 
   spec.add_dependency 'docker-api', '~> 1.33'
-  spec.add_dependency 'rest-client', '~> 2.0'
-  spec.add_dependency 'sensu-plugin', '~> 2.1'
+  spec.add_dependency 'rest-client', '~> 2.1'
+  spec.add_dependency 'sensu-plugin', '~> 4.0'
   spec.add_development_dependency 'bundler', '~> 2.2'
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rspec', '~> 3.7'