v0.6.2

• The used memory is not retrieved via the gem get_process_mem, which is Windows compatible. Ref #114
• Updated various deps (fixes potential exception of activesupport due to old version)
• New Target#error_404_res, and Target#error_404_url (same as Target#non_existant_page_url) methods. The Target#non_existant_url method will be removed in the next major version.