Fix URL in jekyll configuration

Author: kinkie

_config.yml

@@ -1,7 +1,9 @@
 title: "Squid Programming Guide"
 description: "Squid Web Cache programmers' guide"
+url: "https://programming-guide.squid-cache.org/"
 plugins:
-  - jekyll-sitemap
   - jekyll-optional-front-matter
   - jekyll-relative-links
   - jekyll-titles-from-headings
+
+# - jekyll-sitemap