Duplication of files (in wrong dirs) when doing multiple dir copies

Nobody has claimed this yet.

I have a taskfile that has a portion like this:

```js
module.exports.copyProcs = async function copyProcs(task) {
await task.source('procs/**/*.js').target('dist/procs')
await task.source('procs/**/.*').target('dist/procs')
}

module.exports.copyConf = async function copyConf(task) {
await task.source('conf/**/.*').target('dist/conf')
}

module.exports.copyDirs = async function copyDirs(task) {
await task.parallel(['copyProcs', 'copyConf'])
}

module.exports.build = async function build(task) {
// compile is not necessary to show
await task.serial(['compile', 'copyDirs'])
}
```

`taskr build` is my `yarn build`

This should copy all `.js` files and `.` files (specifically `.gitignore`) from `procs` to `dist/procs`

It should also copy all `.` files (specifically `.eslintrc` and `.jscsrc`) from `conf` to `dist/conf`

When run, it is copying `.eslintrc` and `.jscsrc` to _both_ `dist/conf` and `dist/procs`.

If I change the content of `function copyDirs` to `await task.serial(['copyProcs', 'copyConf'])` it works as expected.

Not sure what the reason it.

Start by reproducing the issue with the shown task definitions and run `taskr build`, comparing `copyDirs` with parallel and serial execution. Trace the task runner's handling of concurrent directory-copy operations. Done means `.js` and dotfiles from `procs` appear only in `dist/procs`, while dotfiles from `conf` appear only in `dist/conf` during parallel execution.

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