Replace/remove link to Drone server

The main page for the Drone server of Nextcloud does not provide any
value to a regular user, as it is just a login page. Due to its use in
the Kanban document, its link was replaced by the webpage of the Drone
project itself; in the case of the codereviews document the link was
removed and replaced with a textual explanation about where to find the
results of each pull request build.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

developer_manual/bugtracker/codereviews.rst

@@ -36,8 +36,9 @@ How will it work?
    review.
 #. Before a pull request will be merged into master or the corresponding
    branch at least 2 reviewers need to give :+1 score.
-#. Our `continuous integration server`_ will give an additional indicator for
-   the quality of the pull request.
+#. Our continuous integration server will give an additional indicator for
+   the quality of the pull request (the results can be accessed from the GitHub
+   interface for that pull request).
 
 Examples
 --------
@@ -55,7 +56,6 @@ Questions?
 
 Feel free to drop a line on the `forums`_ or join us on `IRC`_.
 
-.. _continuous integration server: https://drone.weasel.rocks/
 .. _forums: https://help.nextcloud.com/
 .. _IRC: http://webchat.freenode.net/?channels=nextcloud-dev
 .. _coding guidelines: ../general/codingguidelines

developer_manual/bugtracker/kanban.rst

@@ -262,6 +262,6 @@ Release.
 .. _“Given … when … then …“: https://github.com/cucumber/cucumber/wiki/Given-When-Then
 .. _unit tests: https://github.com/nextcloud/server/tree/master/tests
 .. _Code Review Documentation: codereviews
-.. _Drone: https://drone.weasel.rocks
+.. _Drone: https://github.com/drone/drone
 .. _Cucumber: http://cukes.info/
 .. _Transifex: https://www.transifex.com/nextcloud/