Merge #13221: travis: Rename the build stage "check_doc" to "lint"

3d8ae74657 travis: Rename the build stage "check_doc" to "lint" (practicalswift)

Pull request description:

  Rename the Travis build stage from `check_doc` to `lint`.

  When `check_doc` was introduced back in fa1b80db88 it was used to make sure `contrib/devtools/check-doc.py` was run only once.

  Nowadays `check_docs` is used to trigger various linting type jobs which makes the name `check_doc` a bit misleading.

Tree-SHA512: 39d7f3dd2ee6374e60c64fe4366df5f8752e350c4404d2d5b3dd9da64d6ac730a6b523286df4042a14360a5740e068a072ef32e04283ada719c988c7f9a1bf86

.travis.yml

@@ -9,7 +9,7 @@ cache:
   - depends/sdk-sources
   - $HOME/.ccache
 stages:
-  - check_doc
+  - lint
   - test
 env:
   global:
@@ -77,7 +77,7 @@ after_script:
 
 jobs:
   include:
-    - stage: check_doc
+    - stage: lint
       sudo: false
       addons:
         apt: