A regression occurred in 0.2.2 which can be reproduced using:

```js
const assert = require('assert');
const tmp = require('tmp');
tmp.dir({ unsafeCleanup: true }, (err, path, cleanup) => {
  assert.ifError(err);
  cleanup(assert.ifError);
});
```
This works with 0.2.1.  With 0.2.2 it fails with:

    /path/to/tmp/node-tmp/lib/tmp.js:358
            return removeFunction(fileOrDirName, next || function() {});
                   ^

    TypeError: removeFunction is not a function
        at _cleanupCallback (/path/to/tmp/node-tmp/lib/tmp.js:358:16)
        at /path/to/tmp/node-tmp/repro.js:5:3
        at _dirCreated (/path/to/tmp/node-tmp/lib/tmp.js:207:7)
        at FSReqCallback.oncomplete (node:fs:192:23)

This occurs because 00bb5b2 upgraded
the rimraf dependency from ^3.0.0 to ^5.0.5 without handling the change
to a `Promise`-based API in 4.0.0
(isaacs/rimraf@a71e7f9)
or the removal of the default export in 5.0.0
(isaacs/rimraf@c7a3fd4).

This commit fixes the issue by dropping the `rimraf` dependency in favor
of `fs.rm({recursive: true})`.

It also updates the nodejs engine version to 14.14, when `fs.rm()` was
added.

Fixes: 00bb5b2 ("Update rimraf and drop old Node compatibility")
Fixes: raszi#295
Signed-off-by: Kevin Locke <kevin@kevinlocke.name>