Add local config for slack url
diff --git a/docs/conf.py b/docs/conf.py
index fc8aed0..7fe78b3 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -185,3 +185,5 @@
     "default": ("apache/mynewt-documentation", "docs/")
 }
 edit_on_github_branch = 'master'
+
+slack_url = 'https://join.slack.com/t/mynewt/shared_invite/enQtNjA1MTg0NzgyNzg3LTZiYzgxNDQ3NmQ5ZWFkMTY4MjNjYTNmNGJjMDhiMZiMWFjNDdkMzBlNzZjOWY0YzljYTBhYTg1YmRjYzljZDg'
diff --git a/docs/themes/mynewt/footer.html b/docs/themes/mynewt/footer.html
index 1388bbf..94d26af 100644
--- a/docs/themes/mynewt/footer.html
+++ b/docs/themes/mynewt/footer.html
@@ -13,7 +13,7 @@
                 Apache Mynewt, Mynewt, Apache, the Apache feather logo, and the Apache Mynewt project logo are either
                 registered trademarks or trademarks of the Apache Software Foundation in the United States and other countries.
               </small>
-              <a href="{{ config.extra.slack_url }}">
+              <a href="{{ slack_url }}">
                 <img src="{{pathto("_static/img/add_to_slack.png", 1)}}" alt="Slack Icon" title="Join our Slack Community" />
               </a>
           </div>
diff --git a/versions/v1_4_0/mynewt-documentation/docs/themes/mynewt/footer.html b/versions/v1_4_0/mynewt-documentation/docs/themes/mynewt/footer.html
index 1388bbf..94d26af 100644
--- a/versions/v1_4_0/mynewt-documentation/docs/themes/mynewt/footer.html
+++ b/versions/v1_4_0/mynewt-documentation/docs/themes/mynewt/footer.html
@@ -13,7 +13,7 @@
                 Apache Mynewt, Mynewt, Apache, the Apache feather logo, and the Apache Mynewt project logo are either
                 registered trademarks or trademarks of the Apache Software Foundation in the United States and other countries.
               </small>
-              <a href="{{ config.extra.slack_url }}">
+              <a href="{{ slack_url }}">
                 <img src="{{pathto("_static/img/add_to_slack.png", 1)}}" alt="Slack Icon" title="Join our Slack Community" />
               </a>
           </div>
diff --git a/versions/v1_5_0/mynewt-documentation/docs/themes/mynewt/footer.html b/versions/v1_5_0/mynewt-documentation/docs/themes/mynewt/footer.html
index 1388bbf..94d26af 100644
--- a/versions/v1_5_0/mynewt-documentation/docs/themes/mynewt/footer.html
+++ b/versions/v1_5_0/mynewt-documentation/docs/themes/mynewt/footer.html
@@ -13,7 +13,7 @@
                 Apache Mynewt, Mynewt, Apache, the Apache feather logo, and the Apache Mynewt project logo are either
                 registered trademarks or trademarks of the Apache Software Foundation in the United States and other countries.
               </small>
-              <a href="{{ config.extra.slack_url }}">
+              <a href="{{ slack_url }}">
                 <img src="{{pathto("_static/img/add_to_slack.png", 1)}}" alt="Slack Icon" title="Join our Slack Community" />
               </a>
           </div>