move linkcheck to travis (#4544)

* move linkcheck to travis

only run it on master merges just like we do on jenkins

* don't build for a PR
diff --git a/.travis.yml b/.travis.yml
index 87edf43..5b8bbbb 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -138,6 +138,10 @@
           # urllib3 tests fail on xenial for whatever reason
           dist: trusty
           sudo: false
+        - python: 2.7
+          services: docker
+          env: TOXENV=docs-linkcheck DOCKER=pyca/cryptography-runner-buster
+          if: branch = master AND type != pull_request
 
 install:
     - ./.travis/install.sh
diff --git a/Jenkinsfile b/Jenkinsfile
index b9d8698..14a1ed7 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -28,17 +28,6 @@
     ],
 ]
 
-/* Add the linkcheck job to our config list if we're on master */
-if (env.BRANCH_NAME == "master") {
-    configs.add(
-        [
-            label: 'docker',
-            imageName: 'pyca/cryptography-runner-buster',
-            toxenvs: ['docs-linkcheck'],
-        ]
-    )
-}
-
 def checkout_git(label) {
     retry(3) {
         def script = ""