Remove .travis.yml

They changed their free tier and I might as well use GitHub Actions
for ILRI stuff anyways.

.travis.yml

@@ -1,19 +0,0 @@
-os: linux
-arch: arm64-graviton2
-dist: focal
-language: python
-python:
-  - "3.6"
-  - "3.7"
-  - "3.8"
-  - "3.9"
-  - "nightly"
-jobs:
-  allow_failures:
-    - python: "nightly"
-install:
-  - "pip install -r requirements.txt"
-  - "pip install -r requirements-dev.txt"
-script: pytest
-
-# vim: ts=2 sw=2 et