Summary:
Command which transpiles and bundles plugin code.
It is supposed to be used in "prepack" script for all open-sourced plugin packages to bundle them before publishing like this:
```
{
"devDependencies": {
"flipper-pkg": "latest"
},
"scripts": {
"prepack": "flipper-pkg bundle"
}
}
```
Also made directory parameter of other command "pack" optional so it also can be called from plugin directory simply by `flipper-pkg pack`.
Changelog: "flipper-pkg bundle" command for bundling plugins before publishing.
Reviewed By: mweststrate
Differential Revision: D21129691
fbshipit-source-id: 8f97bc950c28cf9ad8b0117c0e1d811ed1b988eb
1491e111c9