Force youtube-dl to use python 3.6

youtube-dl-python-3.6

Since python 2.x will be deprecated in 2020, it is better to use python 3.x for youtube-dl. 
Plus, python 3.6 runs faster. But for ubuntu, normaly, youtube-dl just uses python 2.x. 
Here is how to force youtube-dl to use python 3.6.

*1.Install python3.6 according to this gist:
https://gist.github.com/thodison/3dfcff7d09560357c9c6a9b453e0d6ed

*2.Edit ~/.bashrc
Add the folloing line on the top, then save and close it:
alias python3="python3.6"

then on the terminal, run:
source ~/.bashrc
python3 --version //3.6.4

*3.Completely remove youtube-dl
sudo apt-get remove -y youtube-dl
sudo apt-get autoremove --purge youtube-dl
*Use other commands to find related files and delete them.

*4. Install youtube-dl:
sudo pip3 install youtube-dl
youtube-dl -v # Now youtube-dl is using python 3.6

*5.Upgrade:
sudo pip3 install --upgrade youtube-dl