Fix CI builds to ensure functionality (pytube#690)

- made flake8 compliant
- update stream tests and coverage
- fix problems with playlist file
- added python 3.9 as a test target

.flake8

@@ -1,5 +1,5 @@
 [flake8]
-ignore = E231,E203,W503,Q000,WPS111,WPS305,WPS348,WPS602,D400,DAR201,S101,DAR101,C812,D104,I001,WPS306,WPS214,D401,WPS229,WPS420,WPS230,WPS414,WPS114,WPS226,WPS442,C819,WPS601,T001,RST304,WPS410,WPS428,A003,A002,I003,WPS221,WPS326,WPS201,S405,DAR301,WPS210,WPS202,WPS213,WPS301,P103,WPS407,WPS432,WPS211,S314,S310,S001,IF100,PT001
+ignore = E231,E203,W503,Q000,WPS111,WPS305,WPS348,WPS602,D400,DAR201,S101,DAR101,C812,D104,I001,WPS306,WPS214,D401,WPS229,WPS420,WPS230,WPS414,WPS114,WPS226,WPS442,C819,WPS601,T001,RST304,WPS410,WPS428,A003,A002,I003,WPS221,WPS326,WPS201,S405,DAR301,WPS210,WPS202,WPS213,WPS301,P103,WPS407,WPS432,WPS211,S314,S310,S001,IF100,PT001,PT019
 max-line-length = 95
 
 [isort]

.travis.yml

@@ -6,6 +6,7 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9-dev"
 install: "make"
 script:
   - make ci

Makefile

@@ -43,7 +43,8 @@ ci:
 	pip install pipenv
 	pipenv install --dev --skip-lock
 	pipenv run flake8
-	pipenv run pytest --cov-report term-missing --cov=humps
+	# pipenv run pytest --cov-report term-missing # --cov=humps
+	pipenv run coverage run -m pytest
 
 clean: clean-build clean-pyc
 

Pipfile

@@ -10,6 +10,7 @@ typing_extensions = "*"
 black = "==19.10b0"
 codecov = "*"
 coveralls = "*"
+coverage = "*"
 flake8 = "*"
 flake8-breakpoint = "*"
 flake8-broken-line = "*"