"--report-directory" flag ignored by grunt-cli@~1.4.2

Hi,
I'm trying to upgrade grunt@1.0.1 to a higher version of the library and I'm facing some troubles with grunt recognising the flag _report-directory_. To debug this issue I've used this simple grunt task, that prints all the flags that are being passed:

```js
'use strict';

module.exports = (grunt) => {
grunt.registerTask('grunt_options', 'Runs grunt options debugging', function run() {
console.log('Those are all the grunt options: ', grunt.option.flags());
});
};
```

With some trial and error, I've been able to track down where this regression seems to have happened:

1. Run `npm i grunt@1.3.0 --save-dev`
2. Execute grunt task `node/node node_modules/.bin/grunt grunt_options --report-directory=1 --report-dy=2 --report-wd-directory=3`
3. Uninstall grunt@1.3.0 and install 1.4.0 `npm uninstall grunt && npm i grunt@1.4.0`
4. Run the task in step 2

For `grunt@1.3.0` the output of the task is:
```
Those are all the grunt options: [
'--report-directory=1',
'--report-dy=2',
'--report-wd-directory=3',
'--gruntfile=/Users/roguib/dev/visual-builder/mcs_buf/breeze/vbcs-client/Gruntfile.js'
]
```

However, for `grunt@1.4.0` the output no longer includes `--report-directory` flag:

```
Running "grunt_options" task
Those are all the grunt options: [
'--report-dy=2',
'--report-wd-directory=3',
'--no-respawning',
'--gruntfile=/Users/roguib/dev/visual-builder/mcs_buf/breeze/vbcs-client/Gruntfile.js'
]
```

I've noticed by looking at the diff [v1.3.0...v1.4.0](https://github.com/gruntjs/grunt/compare/v1.3.0...v1.4.0) it could be caused by a regression in `grunt-cli` library. Adding an override to `grunt-cli` to `~1.3.2` instead of the `~1.4.2` version that comes with the new release seems to solve the issue:
```
"overrides": {
"grunt": {
"grunt-cli": "~1.3.2"
}
},
```

In that case, the task correctly identifies `--report-directory` flag:
```
Those are all the grunt options: [
'--report-directory=1',
'--report-dy=2',
'--report-wd-directory=3',
'--gruntfile=/Users/roguib/dev/visual-builder/mcs_buf/breeze/vbcs-client/Gruntfile.js'
]
```

This problem is also reproducible with the latest release of `grunt@1.6.0` and `grunt-cli@~1.4.3`.