update rake dependency

Author: geemus

fog-openstack.gemspec

@@ -31,7 +31,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "mime-types-data"
   spec.add_development_dependency 'minitest'
   spec.add_development_dependency 'pry-byebug'
-  spec.add_development_dependency 'rake',    '~> 10.0'
+  spec.add_development_dependency 'rake',    '>= 12.3.3'
   spec.add_development_dependency 'rubocop'
   spec.add_development_dependency 'shindo',  '~> 0.3'
   spec.add_development_dependency 'vcr'