Use GitHub Actions for CI (#802)

Travis-CI recently made changes to their service model, and pytube is likely to exceed their free credits. This PR migrates the functionality provided by Travis CI to GitHub's CI offering, which is free for public repositories.

.github/workflows/ci.yml

@@ -0,0 +1,39 @@
+name: CI testing
+
+on:
+  pull_request:
+    branches: [ master ]
+    paths-ignore:
+      - '**/README.md'
+      - 'docs/**'
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        python: [3.5, 3.6, 3.7, 3.8]
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Setup python
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python }}
+
+      - name: Upgrade pip
+        run: pip install --upgrade pipenv
+
+      - name: Run make ci
+        run: make ci
+
+      # https://github.com/codecov/codecov-action
+      - name: Codecov
+        uses: codecov/codecov-action@v1
+        with:
+          file: .coverage
+          fail_ci_if_error: true
+          

.travis.yml

@@ -1,20 +0,0 @@
-language: python
-cache:
-  - apt
-  - pip
-python:
-  - "3.6"
-  - "3.7"
-  - "3.8"
-  - "3.9-dev"
-install: "make"
-script:
-  - make ci
-before_install:
-  - pip install pipenv --upgrade
-sudo: false
-after_success:
-  - codecov
-  - coveralls
-notifications:
-#  slack: watchcloud:rNoT5kJJakPqwLSKuev6oa4C

README.md

@@ -10,7 +10,7 @@ Ping @ronncc if you would like to help out
 	  <img src="https://img.shields.io/pypi/v/pytube.svg" alt="pypi">
 	  <a href="https://travis-ci.org/nficano/pytube"><img src="https://travis-ci.org/nficano/pytube.svg?branch=master" /></a>
 	  <a href="http://python-pytube.readthedocs.io/en/latest/?badge=latest"><img src="https://readthedocs.org/projects/python-pytube/badge/?version=latest" /></a>
-	  <a href="https://coveralls.io/github/nficano/pytube?branch=master"><img src="https://coveralls.io/repos/github/nficano/pytube/badge.svg?branch=master#23e6f7ac56dd3bde" /></a>
+	  <a href="https://codecov.io/gh/nficano/pytube"><img src="https://codecov.io/gh/nficano/pytube/branch/master/graph/badge.svg" /></a>
       <a href="https://pypi.org/project/pytube/"><img src="https://img.shields.io/pypi/dm/pytube.svg" alt="pypi"></a>
 	  <a href="https://pypi.python.org/pypi/pytube/"><img src="https://img.shields.io/pypi/pyversions/pytube.svg" /></a>
     <p>