Fix handling of cli arg that is symlink

[jeremywiebe]

Summary
I've had trouble running checksync for quite a while. I had to resort to running it by passing the entrypoint file to node manually node path/to/checksync.js.

The error I'd see is this:

(node:45761) UnhandledPromiseRejectionWarning: Error: ENOTDIR: not a directory, scandir '/Users/jeremy/.volta/tools/image/packages/checksync/bin/checksync'
(node:45761) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:45761) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Issues
I haven't raised an issue for this. I can, if you'd like. :)

Details

I finally traced the error to how symlinks are resolved for unrecognized args.

The process sees a __filename of /Users/jeremy/.volta/tools/image/packages/checksync/bin/checksync. On my system, fs.readlinkSync(__filename) returns ../lib/node_modules/.bin/checksync. When path.resolve() resolves that path, it ends up at a path that doesn't exist on my system because it joins process.cwd() with the relative path passed to path.resolve().

I think the fix is just to use fs.realpathSync() which appears to resolve to the right path on my system.

Screenshots
If applicable, add screenshots to help illustrate your changes

Review notes
Add additional context for reviewers here. Consider what, if anything, needs particular attention paid to it.
If this is a draft, perhaps clarify what work remains and what, if anything, is ready for review.

[codecov]

Codecov Report

Merging #659 (380fc1b) into main (29903e5) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #659   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files          30       30           
  Lines         549      549           
  Branches      108      108           
=======================================
  Hits          548      548           
  Misses          1        1           

Impacted Files	Coverage Δ
src/cli.js	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 29903e5...380fc1b. Read the comment docs.

[somewhatabstract]

LGTM

[somewhatabstract]

I cannot remember why I did not use this originally - I do remember there was a reason. lol

Helpful, huh?