Refactor AR::Tasks::DatabaseTasks::migrate

Set consistent type cast ENV["VERBOSE"]:
  ENV["VERBOSE"] is true if it not equal "false"

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -164,7 +164,7 @@ def drop_current(environment = env)
       def migrate
         raise "Empty VERSION provided" if ENV["VERSION"] && ENV["VERSION"].empty?
 
-        verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true
+        verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] != "false" : true
         version = ENV["VERSION"] ? ENV["VERSION"].to_i : nil
         scope = ENV["SCOPE"]
         verbose_was, Migration.verbose = Migration.verbose, verbose