Make venv-activate.sh compatible with sh and zsh

[notdefine]

Description

Make venv-activate.sh compatible with sh and zsh

How to test

$ if [ "$0" == "$BASH_SOURCE" ]; then echo "a"; fi
Error: sh: 1: [: sh: unexpected operator

$ if [[ "$0" == "$BASH_SOURCE" ]]; then echo "a"; fi
Succed

Contributor license agreement signed?

CLA [X] (Whether you have signed a CLA - Contributor Licensing Agreement

[devs-mycroft]

Hello, @notdefine, thank you for helping with the Mycroft project! We welcome everyone
into the community and greatly appreciate your help as we work to build an AI
for Everyone.

To protect yourself, the project, and users of Mycroft technologies we require
a Contributor Licensing Agreement (CLA) before accepting any code
contribution. This agreement makes it crystal clear that along with your
code you are offering a license to use it within the confines of this project.
You retain ownership of the code, this is just a license.

Please visit https://mycroft.ai/cla to initiate this one-time signing. Thank
you!

[forslund]

Thanks for taking noticing and fixing this. Will merge after the CLA is handled.

[notdefine]

Hello, the CLA process was clear and easy, just signed it, greetings Thomas

[krisgesling]

CLA received, thanks Thomas :)

[forslund]

Re-verified this. It's definitely better bash code. And if it works in more shells it's better (only had dash available on this computer and that doesn't work for a bunch of other reasons).

Merging this now. Thank you.