Fix Facebook share link

Fixes #323.

lib/app.rb

@@ -230,7 +230,7 @@ class App < Sinatra::Application
     '/s/jetbrains/web'    => 'https://www.jetbrains.com/webstorm/?utm_source=devdocs&utm_medium=sponsorship&utm_campaign=devdocs',
     '/s/code-school'      => 'http://www.codeschool.com/?utm_campaign=devdocs&utm_content=homepage&utm_source=devdocs&utm_medium=sponsorship',
     '/s/tw'               => 'https://twitter.com/intent/tweet?url=http%3A%2F%2Fdevdocs.io&via=DevDocs&text=All-in-one%2C%20offline%20API%20documentation%20browser%3A',
-    '/s/fb'               => 'https://twitter.com/intent/tweet?url=http%3A%2F%2Fdevdocs.io&via=DevDocs&text=All-in-one%2C%20offline%20API%20documentation%20browser%3A',
+    '/s/fb'               => 'https://www.facebook.com/sharer/sharer.php?u=http%3A%2F%2Fdevdocs.io',
     '/s/re'               => 'http://www.reddit.com/submit?url=http%3A%2F%2Fdevdocs.io&title=All-in-one%2C%20offline%20API%20documentation%20browser&resubmit=true'
   }.each do |path, url|
     class_eval <<-CODE, __FILE__, __LINE__ + 1