Drop or replace references to Travis CI (#236)

- Update Maven's `ciManagement` section to refer to GitHub Actions.
- Drop an obsolete "wish list" entry.

error-prone-contrib/README.md

@@ -76,8 +76,7 @@ project:
 - Document how to enable the checks.
 - Document how to apply patches.
 - Document each of the checks.
-- Add Travis CI, [SonarQube][sonarcloud] and [Codecov][codecov]
-  integrations.
+- Add [SonarQube][sonarcloud] and [Codecov][codecov] integrations.
 - Investigate whether it makes sense to include license headers in each file.
   If so, set that up and enforce it.
 - Add non-Java file formatting support, like we have internally at Picnic.

pom.xml

@@ -56,8 +56,8 @@
         <url>https://github.com/PicnicSupermarket/error-prone-support/issues</url>
     </issueManagement>
     <ciManagement>
-        <system>Travis CI</system>
-        <url>https://travis-ci.org/PicnicSupermarket/error-prone-support</url>
+        <system>GitHub Actions</system>
+        <url>https://github.com/PicnicSupermarket/error-prone-support/actions</url>
     </ciManagement>
     <distributionManagement>
         <repository>