Enable rules which were disabled during bugfix release

src/ameba/rule/lint/bad_directive.cr

@@ -21,7 +21,6 @@ module Ameba::Rule::Lint
   struct BadDirective < Base
     properties do
       description "Reports bad comment directives"
-      enabled false
     end
 
     AVAILABLE_ACTIONS = InlineComments::Action.names.map(&.downcase)

src/ameba/rule/style/is_a_nil.cr

@@ -23,7 +23,6 @@ module Ameba::Rule::Style
   struct IsANil < Base
     properties do
       description "Disallows calls to `is_a?(Nil)` in favor of `nil?`"
-      enabled false
     end
 
     MSG            = "Use `nil?` instead of `is_a?(Nil)`"