Update watch.js

This fixes #399, fixes #392, fixes #376 by make the drive letter upper-case.

This is caused by `path.join`, the returned path has a lower-cased drive letter:
```text
> path.join('C:\\', 'Test')
'c:\\Test'
```

Later check path against rules using minimatch, it failed as `options.nocase` is `false` by default.