Improve Travis configuration file and fix file name

Author: Cito

.travis.yml

@@ -0,0 +1,30 @@
+language: python
+matrix:
+  include:
+    - name: Code quality tests
+      env: TOXENV=black,flake8,pylint,manifest
+      python: 3.8
+    - name: Unit tests with Python 3.8
+      env: TOXENV=py38
+      python: 3.8
+    - name: Unit tests with Python 3.7
+      env: TOXENV=py37
+      python: 3.7
+    - name: Unit tests with Python 3.6
+      env: TOXENV=py36
+      python: 3.6
+    - name: Unit tests with PyPy 3
+      env: TOXENV=pypy3
+      python: pypy3
+cache:
+  directories:
+    - "$HOME/.cache/pip"
+    - "$TRAVIS_BUILD_DIR/.tox"
+install:
+  - pip install tox
+  - pip install -e .[test]
+  - pip install pytest-cov codecov
+script:
+  - tox -e $TOXENV -- --cov-branch --cov-report=term-missing --cov=aiohttp_graphql
+after_success:
+  - codecov