Cleanup ameba warnings (#551)

src/kemal/ext/response.cr

@@ -1,6 +1,7 @@
 class HTTP::Server::Response
   class Output
     def close
+      # ameba:disable Style/NegatedConditionsInUnless
       unless response.wrote_headers? && !response.headers.has_key?("Content-Range")
         response.content_length = @out_count
       end

src/kemal/static_file_handler.cr

@@ -4,6 +4,7 @@
 
 module Kemal
   class StaticFileHandler < HTTP::StaticFileHandler
+    # ameba:disable Metrics/CyclomaticComplexity
     def call(context : HTTP::Server::Context)
       return call_next(context) if context.request.path.not_nil! == "/"