Update API version to v19.0

Author: wynksaiddestroy

README.md

@@ -60,14 +60,14 @@ end
 
 ### API Version
 
-OmniAuth Facebook uses versioned API endpoints by default (current v5.0). You can configure a different version via `client_options` hash passed to `provider`, specifically you should change the version in the `site` and `authorize_url` parameters. For example, to change to v7.0 (assuming that exists):
+OmniAuth Facebook uses versioned API endpoints by default (current v19.0). You can configure a different version via `client_options` hash passed to `provider`, specifically you should change the version in the `site` and `authorize_url` parameters. For example, to change to v20.0 (assuming that exists):
 
 ```ruby
 use OmniAuth::Builder do
   provider :facebook, ENV['FACEBOOK_APP_ID'], ENV['FACEBOOK_APP_SECRET'],
     client_options: {
-      site: 'https://graph.facebook.com/v7.0',
-      authorize_url: "https://www.facebook.com/v7.0/dialog/oauth"
+      site: 'https://graph.facebook.com/v20.0',
+      authorize_url: "https://www.facebook.com/v20.0/dialog/oauth"
     }
 end
 ```

lib/omniauth/strategies/facebook.rb

@@ -10,7 +10,7 @@ class Facebook < OmniAuth::Strategies::OAuth2
       class NoAuthorizationCodeError < StandardError; end
 
       DEFAULT_SCOPE = 'email'
-      DEFAULT_FACEBOOK_API_VERSION = 'v5.0'.freeze
+      DEFAULT_FACEBOOK_API_VERSION = 'v19.0'.freeze
 
       option :client_options, {
         site: "https://graph.facebook.com/#{DEFAULT_FACEBOOK_API_VERSION}",