Simplify CI config now that wxPython has been removed

.travis.yml

@@ -5,47 +5,29 @@ matrix:
     - python: 2.7
       name: "Test Python 2.7"
       env: TOXENV=py27
-      before_install:
-        - sudo apt-get update
-        - sudo apt-get install -y build-essential python-dev libgtk-3-dev      
       install: pip install tox
-      script: tox -vvvvv
+      script: tox
     - python: 3.6
       name: "Test Python 3.6"
       env: TOXENV=py36
-      before_install:
-        # Install neccessary Linux dependencies to build wxPython from source.
-        - sudo apt-get update
-        - sudo apt-get install -y build-essential python3-dev libgtk-3-dev
       install: pip install tox
       script:
-        # Pass -vvv to pip through tox because wxPython can take ~20min to build and
-        # Travis CI thinks that the build has stalled unless build progress is output.
-        - tox -vvvvv
+        - tox
     - python: 3.7
       name: "Test Python 3.7"
       env: TOXENV=py37
-      before_install:
-        - sudo apt-get update
-        - sudo apt-get install -y build-essential python3-dev libgtk-3-dev
       install: pip install tox
-      script: tox -vvvvv
+      script: tox
     - python: 3.8
       name: "Test Python 3.8"
       env: TOXENV=py38
-      before_install:
-        - sudo apt-get update
-        - sudo apt-get install -y build-essential python3-dev libgtk-3-dev
       install: pip install tox
-      script: tox -vvvvv
+      script: tox
     - python: pypy3
       name: "Test PyPy3"
       env: TOXENV=pypy3
-      before_install:
-        - sudo apt-get update
-        - sudo apt-get install -y build-essential python3-dev libgtk-3-dev
       install: pip install tox
-      script: tox -vvvvv
+      script: tox
     - python: 3.6
       name: "Check formatting"
       install: pip install black isort