Remove broken link and update CircleCI's name (#32448)

docs/tutorial/testing-on-headless-ci.md

@@ -3,7 +3,7 @@
 Being based on Chromium, Electron requires a display driver to function.
 If Chromium can't find a display driver, Electron will fail to launch -
 and therefore not executing any of your tests, regardless of how you are running
-them. Testing Electron-based apps on Travis, Circle, Jenkins or similar Systems
+them. Testing Electron-based apps on Travis, CircleCI, Jenkins or similar Systems
 requires therefore a little bit of configuration. In essence, we need to use
 a virtual display driver.
 
@@ -49,10 +49,9 @@ install:
 
 For Jenkins, a [Xvfb plugin is available](https://wiki.jenkins-ci.org/display/JENKINS/Xvfb+Plugin).
 
-### Circle CI
+### CircleCI
 
-Circle CI is awesome and has Xvfb and `$DISPLAY`
-[already set up, so no further configuration is required](https://circleci.com/docs/environment#browsers).
+CircleCI is awesome and has Xvfb and `$DISPLAY` already set up, so no further configuration is required.
 
 ### AppVeyor