doc: Drop mentions of Travis CI as it is no longer used

README.md

@@ -56,7 +56,8 @@ There are also [regression and integration tests](/test), written
 in Python, that are run automatically on the build server.
 These tests can be run (if the [test dependencies](/test) are installed) with: `test/functional/test_runner.py`
 
-The Travis CI system makes sure that every pull request is built for Windows, Linux, and macOS, and that unit/sanity tests are run automatically.
+The CI (Continuous Integration) systems make sure that every pull request is built for Windows, Linux, and macOS,
+and that unit/sanity tests are run automatically.
 
 ### Manual Quality Assurance (QA) Testing
 

doc/developer-notes.md

@@ -543,7 +543,7 @@ General Bitcoin Core
   - *Rationale*: RPC allows for better automatic testing. The test suite for
     the GUI is very limited.
 
-- Make sure pull requests pass Travis CI before merging.
+- Make sure pull requests pass CI before merging.
 
   - *Rationale*: Makes sure that they pass thorough testing, and that the tester will keep passing
      on the master branch. Otherwise, all new pull requests will start failing the tests, resulting in
@@ -1036,7 +1036,7 @@ Scripted diffs
 --------------
 
 For reformatting and refactoring commits where the changes can be easily automated using a bash script, we use
-scripted-diff commits. The bash script is included in the commit message and our Travis CI job checks that
+scripted-diff commits. The bash script is included in the commit message and our CI job checks that
 the result of the script is identical to the commit. This aids reviewers since they can verify that the script
 does exactly what it is supposed to do. It is also helpful for rebasing (since the same script can just be re-run
 on the new master commit).

doc/release-process.md

@@ -307,9 +307,9 @@ bitcoin.org (see below for bitcoin.org update instructions).
   - First, check to see if the Bitcoin.org maintainers have prepared a
     release: https://github.com/bitcoin-dot-org/bitcoin.org/labels/Core
 
-      - If they have, it will have previously failed their Travis CI
+      - If they have, it will have previously failed their CI
         checks because the final release files weren't uploaded.
-        Trigger a Travis CI rebuild---if it passes, merge.
+        Trigger a CI rebuild---if it passes, merge.
 
   - If they have not prepared a release, follow the Bitcoin.org release
     instructions: https://github.com/bitcoin-dot-org/bitcoin.org/blob/master/docs/adding-events-release-notes-and-alerts.md#release-notes

test/functional/README.md

@@ -23,7 +23,7 @@ don't have test cases for.
 - The oldest supported Python version is specified in [doc/dependencies.md](/doc/dependencies.md).
   Consider using [pyenv](https://github.com/pyenv/pyenv), which checks [.python-version](/.python-version),
   to prevent accidentally introducing modern syntax from an unsupported Python version.
-  The Travis linter also checks this, but [possibly not in all cases](https://github.com/bitcoin/bitcoin/pull/14884#discussion_r239585126).
+  The CI linter job also checks this, but [possibly not in all cases](https://github.com/bitcoin/bitcoin/pull/14884#discussion_r239585126).
 - See [the python lint script](/test/lint/lint-python.sh) that checks for violations that
   could lead to bugs and issues in the test code.
 - Use [type hints](https://docs.python.org/3/library/typing.html) in your code to improve code readability