Remove references about Rails 5, that's not supported anymore

Author: markoudev

README.md

@@ -134,12 +134,6 @@ by default. But it's good to be aware of this in case you're running into
 weirdness.
 
 
-# Known issues
-  * With Rails 5.0 in combination with uniqueness validations, ActiveRecord
-    generates a wrong query. The `x` in front of the queried value, which casts
-    the value to the proper data type, is missing.
-
-
 # Contributing
 To start coding on `mysql-binuuid-rails`, fork the project, clone it locally
 and then run `bin/setup` to get up and running. If you want to fool around in

test/integration/mysql_integration_test.rb

@@ -53,10 +53,6 @@ class BeforePersistedTest < MySQLIntegrationTest
     end
 
     test "validates uniqueness" do
-      if ActiveRecord.version < Gem::Version.new("5.1.0")
-        skip("Skipping uniqueness validation test, known issue on Rails/ActiveRecord 5.0")
-      end
-
       uuid = SecureRandom.uuid
       MyUuidModelWithValidations.create!(the_uuid: uuid)
       duplicate = MyUuidModelWithValidations.new(the_uuid: uuid)