Composer conflict when installing craftcms/plugin-installer I have installed composer successfully but when I try to add:

composer require craftcms/plugin-installer


I get the following:

Your requirements could not be resolved to an installable set of packages.

Problem 1
- craftcms/cms 3.0.0-RC4 requires craftcms/plugin-installer ~1.5.0 -&gt; satisfiable by craftcms/plugin-installer[1.5.0, 1.5.1, 1.5.2] but these conflict with your requirements or minimum-stability.
- craftcms/cms 3.0.0-RC4 requires craftcms/plugin-installer ~1.5.0 -&gt; satisfiable by craftcms/plugin-installer[1.5.0, 1.5.1, 1.5.2] but these conflict with your requirements or minimum-stability.
- craftcms/cms 3.0.0-RC4 requires craftcms/plugin-installer ~1.5.0 -&gt; satisfiable by craftcms/plugin-installer[1.5.0, 1.5.1, 1.5.2] but these conflict with your requirements or minimum-stability.
- Installation request for craftcms/cms 3.0.0-RC4 -&gt; satisfiable by craftcms/cms[3.0.0-RC4].

Installation failed, reverting ./composer.json to its original content.


I have also tried the following with no luck:

composer require craftcms/plugin-installer --ignore-platform-regs


Note my composer.json file shows the following:

{

"minimum-stability": "dev",
"repositories": [
    {
        "type": "composer",
        "url": "https://asset-packagist.org"
    }
],
"config": {
    "optimize-autoloader": true,
    "platform":{
        "php":"7.1.1"
    }
},
"require": {
    "craftcms/cms": "3.0.0-RC4"
}
}


Any help would be appreciated! On a side note this is a local install using Mamp Pro.
I had the same problem following that video, i assume the ReleaseCandidate upgrade differs from the beta upgrade. Following the instructions from the craftcms github repo worked for me. https://docs.craftcms.com/v3/upgrade.html