Bump Bundler version

Author: mark-dce

iiif_manifest.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'activesupport', '>= 4'
 
   spec.add_development_dependency 'bixby', '~> 1.0'
-  spec.add_development_dependency 'bundler', '~> 1.11'
+  spec.add_development_dependency 'bundler', '~> 2.0'
   spec.add_development_dependency 'pry-byebug'
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rspec', '~> 3.0'