Fix pre-build issues [Travis CI]

[areebbeigh]

I'm submitting a ...

• bug report
• feature request

Currently the Travis builds are failing before running the tests at the following points during linting:

• /app/scrapers/yahoo.py:82:17

$ flake8 . --count --max-complexity=16 --show-source --statistics
./app/server.py:12:1: F841 local variable 'e' is assigned to but never used
except Exception as e:
^
./app/scrapers/yahoo.py:82:17: W605 invalid escape sequence '\d'
            cleanl = re.compile('&#[\d]+(;)')
                ^
1     F841 local variable 'e' is assigned to but never used
1     W605 invalid escape sequence '\d'

• ./app/server.py:12:1

$ flake8 . --count --max-complexity=16 --show-source --statistics
./app/server.py:12:1: F841 local variable 'e' is assigned to but never used
except Exception as e:
^
1     F841 local variable 'e' is assigned to but never used

Before running tests:

• There's also a dependency clash in dev packages preventing pytest-cov>=2.6.0 from being loaded.

I've already fixed these pre-build issues and Travis is successfully moving on to running the actual tests (which are failing due to other reasons).

[areebbeigh]

I'll create a PR after confirmation from maintainers.