Fix use of tmp.dir() with dir option

[fflorent]

Context

Passing the dir option to tmp.dir() results in a strange error:

> var tmp = require('./lib/tmp')
undefined
> var os = require('os')
undefined
> tmp.dir({dir: os.tmpdir()}, (err, val) => { console.log(err, val); })
undefined
> [Error: ENOENT: no such file or directory, lstat '/home/florentpro/projects/node-tmp/[object Object]'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'lstat',
  path: '/home/florentpro/projects/node-tmp/[object Object]'
} undefined

Fix proposal

1. When reading the code, I could find that this line is the culprit (path is defined but refers to the node:path library):

   node-tmp/lib/tmp.js

   Line 469 in 08fa3ab

   fs.realpath(path, cb);

2. When running the tests, istanbul suggests that this line is only executed 2 times, and only for errors, I add a test case to inbandStandard to check passing the dir option

My guess is that the variable that should have been used is pathToResolve like in the implementation of _resolvePathSync:

node-tmp/lib/tmp.js

Line 487 in 08fa3ab

return fs.realpathSync(pathToResolve);

The new tests fail without the fix and pass with the fix.

[raszi]

Great catch! Thank you!

[raszi]

Released as v2.0.5