Change which to command -v

[shadowspawn]

Pull Request Template:

Describe what you did

Fix some issues on an OS without which, such as Centos docker image.

How you did it

Changed which to command -v in the check_current_version routine.

Also added speech marks around variable dereference to fix error message that occurred before fixing above.

How to verify it doesn't effect the functionality of n

Checked n and n prune on MacOS and Centos.

If this solves an issue, please put issue in PR notes.

If this solves an issue, please include the output of issue that had problems and then the fixed output from the same command.

Before (with no which command):

# n prune
/usr/local/bin/n: line 263: which: command not found
/usr/local/bin/n: line 263: which: command not found
/usr/local/bin/n: line 625: [: node/10.12.0: unary operator expected

After:

# n prune

Squash any unnecessary commits to keep history clean as possible

Place description for the changelog in PR so we can tally all changes for any future release

Remove use of which and use generally available command -v.

[troy0820]

This looks good. I'm going to try to pull it in today but trying to do them one at a time is interesting with the order I need them to work.