Install dev extras for travis

Author: multimeric

.travis.yml

@@ -6,7 +6,7 @@ python:
   - '3.6'
   - 'pypy3'
 script:
-  - pip install .
+  - pip install .[dev]
   - coverage run --source flask_rest_jsonapi -m pytest -v
 after_success:
   - coveralls

setup.py

@@ -33,10 +33,10 @@
     setup_requires=['pytest-runner'],
     tests_require=['pytest'],
     extras_require={
-        'tests': [
-        'pytest',
-        'coveralls',
-        'coverage'
+        'dev': [
+            'pytest',
+            'coveralls',
+            'coverage'
         ],
         'docs': 'sphinx'
     }