Removing travis

- All CI is now covered by Github Actions
- Remove .travis.yml
- Remove tox-travis in requirements-extra.txt

.travis.yml

@@ -1,27 +0,0 @@
-sudo: false
-language: python
-install: 
-  - pip3 install -r requirements.txt -r requirements-extra.txt
-script: tox
-matrix:
-  include:
-    - os: "linux"
-      dist: "xenial"
-      python: "3.6"
-    - os: "linux"
-      dist: "xenial"
-      python: "3.7"
-    - os: "linux"
-      dist: "focal"
-      python: "3.8"
-    - os: "linux"
-      dist: "focal"
-      python: "3.9"
-    - os: "windows"
-      language: shell
-      python: "3.9"
-      env: "PATH=/c/python39:/c/python39/Scripts:$PATH"
-      before_install:
-              - choco install python --version=3.9.6
-              - cp /c/python39/python.exe /c/python39/python3.exe
-      script: tox -e py39

requirements-extra.txt

@@ -1,5 +1,4 @@
 pytest>=6,<7
 flake8
-tox-travis
 black
 pyinstaller>=4.5,<5.0; sys_platform != 'linux'