disable travis ci (after setting up github actions)

https://github.com/fphammerle/freesurfer-surface/commit/050804d24063650ed4e5c09857a831557abf2eac

.travis.yml

@@ -1,24 +0,0 @@
-language: python
-
-python:
-- 3.5
-- 3.6
-- 3.7
-
-# required for python >= 3.7
-dist: xenial
-
-install:
-- pip install pipenv
-- pipenv sync --dev
-- pipenv graph
-
-script:
-- pipenv run pytest --cov=freesurfer_surface --cov-report=term-missing --cov-fail-under=100
-- pipenv run pylint --load-plugins=pylint_import_requirements freesurfer_surface
-- pipenv run pylint tests/*
-- pipenv run mypy freesurfer_surface tests
-
-after_success:
-- pip install coveralls
-- coveralls