Persist node version choice on Mac/Linux

[elsassph]

Fixes #24

Implementation:

• when adding -Persist, the version is written to a default file (similar to .nvmrc) in the vs folder where the node binaries are downloaded,
• depending on the scope (User, Machine) a call to Set-NodeVersion (without arguments) is appended to the appropriate profile.ps1.
• Set-NodeVersion when called without version parameter will fallback to the version written in the default file.

Notes:

• This is similar to the way nvm-sh functions (storing the version in a default file and setting the path when the user profile scripts is executed),
• It may be worth documenting how to set the Machine configuration as it requires escalation:

sudo pwsh -c 'Set-NodeVersion 10 -Persist Machine'

[elsassph]

Not sure why tests don't pass... I'll need to try with Windows maybe.

[aaronpowell]

sigh

Looks like something has changed in Travis since last set of build runs. Maybe we should move to GitHub actions 😜

[aaronpowell]

@felixfbecker are you able to run the tests locally on a mac? I can try Windows next week.

[elsassph]

Any progress?

[aaronpowell]

And released as 2.5.1 (I stuffed up the GitHub Actions for 2.5.0 so it didn't deploy 🤣)