This is from pylint. You can generate a pylint config file in the root of your project with this command: 

pylint --generate-rcfile > .pylintrc

Add cv2 so you end up with

# A comma-separated list of package or module names from where C extensions may
# be loaded. Extensions are loading into the active Python interpreter and may
# run arbitrary code.
extension-pkg-whitelist=cv2

Save the file. The lint errors should disappear.