update readme to require 4.0

readme.txt

@@ -2,7 +2,7 @@
 Contributors: hallsofmontezuma, wpsmort, dougal, pbaylies, arnaudbroes
 Donate link: https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=mrtorbert%40gmail%2ecom&item_name=All%20In%20One%20SEO%20Pack&item_number=Support%20Open%20Source&no_shipping=0&no_note=1&tax=0&currency_code=USD&lc=US&bn=PP%2dDonationsBF&charset=UTF%2d8
 Tags: seo, all in one seo, google, twitter, page, image seo, social, search engine optimization, sitemap, WordPress SEO, meta, meta description, xml sitemap, google sitemap, sitemaps, robots meta, yahoo, bing, news sitemaps, multisite, canonical, nofollow, noindex, keywords, description, webmaster tools, google webmaster tools, google analytics
-Requires at least: 3.4
+Requires at least: 4.0
 Tested up to: 4.6
 Stable tag: 2.3.9.1
 License: GPLv2 or later