chore: remove Travis CI configuration

Travis CI is no longer used for this project.

🤖 Generated with Claude Code (https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

.travis.yml

@@ -1,18 +0,0 @@
-language: python
-
-python:
-  - "3.6"
-
-script:
-  - python sort.py
-  - cp README.md docs/index.md
-  - mkdocs build
-
-deploy:
-  provider: pages
-  local-dir: site
-  skip-cleanup: true
-  keep-history: true
-  github-token: $GITHUB_TOKEN
-  on:
-    branch: master