Bumped devise dependency version and fixed kerberos adapter return true for invalid credentials

devise-kerberos-authenticatable.gemspec

@@ -14,5 +14,5 @@ Gem::Specification.new do |s|
   s.homepage        = 'http://www.github.com/atomaka/devise-kerberos-authenticatable'
 
   s.add_dependency  'timfel-krb5-auth', '~> 0.8'
-  s.add_dependency  'devise', '~> 2.2.3'
+  s.add_dependency  'devise', '~> 3.1.1'
 end

lib/devise_kerberos_authenticatable/kerberos_adapter.rb

@@ -12,10 +12,10 @@ module Devise
       begin
         krb5.get_init_creds_password(username, password)
       rescue Krb5Auth::Krb5::Exception
-        false
+        return false
       end
 
-      true
+      return true
     end
   end
 end