Enable rails 6.1 (#1446)

Author: MaicolBen

devise_token_auth.gemspec

@@ -22,7 +22,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = ">= 2.2.0"
 
-  s.add_dependency 'rails', '>= 4.2.0', '< 6.1'
+  s.add_dependency 'rails', '>= 4.2.0', '< 6.2'
   s.add_dependency 'devise', '> 3.5.2', '< 5'
   s.add_dependency 'bcrypt', '~> 3.0'