Don't mention lowest supported AR version

I don't want to have to keep remembering to bump it up whenever I drop
support for oldest versions.

README.md

@@ -8,11 +8,11 @@ This can be useful if you want to use a library that uses Sequel (e.g.
 or if you just want to use Sequel for more complex queries, and you want to
 avoid creating new database connections.
 
-It works on ActiveRecord 4.2+ and fully supports PostgresSQL, MySQL and SQLite,
-both the native adapters and JDBC (JRuby). The [SQL Server] external adapter is
-supported as well (`tinytds` in Sequel), and there is attempted support for
-[Oracle enhanced] (`oracle` and in Sequel). Other adapters might work too, but
-their integration hasn't been tested.
+It fully supports PostgreSQL, MySQL and SQLite adapters, both the native ones
+and JDBC (JRuby). The [SQL Server] external adapter is supported as well
+(`tinytds` in Sequel), and there is attempted support for [Oracle enhanced]
+(`oracle` and in Sequel). Other adapters might work too, but their integration
+hasn't been tested.
 
 ## Why reuse the database connection?