Merge branch 'nonfree'

Use wildcards to match the artifact file (*.whl)

Change the artifact path

Update .travis.yml

Set skip_cleanup to true

reformat .travis.yml

Add tags=true to .travis.yml

1. Add file_glob to .travis.yml

2. only build opencv from python 3.5 and 3.6

Upload the wheel to github release

update variable value

bump OpenCV to 3.4.3