Added actual call to -dev requirements to travis file

.travis.yml

@@ -5,8 +5,9 @@ python:
 # command to install dependencies
 install: 
   - "pip install -r requirements.txt"
+  - "pip install -r requirements-dev.txt"
   - "pip install codecov"
 # command to run tests
 script: "pytest"
 after_success:
-- codecov
\ No newline at end of file
+- codecov