[CI] Fixed merge conflict in .travis.yml

Fixed merge conflict in .travis.yml introduced in 687703a75ed741464e15b71a1e576c319865f3fd

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Doc PR        | none