get processManagers() {
        if (!this.pkg || !this.pkg['ghost-cli'] || !this.pkg['ghost-cli']['process-managers']) {
            return {};
        }

        return mapValues(this.pkg['ghost-cli']['process-managers'], relPath => path.join(this.dir, relPath));
    }
Gets the available process managers (if any) from this extension
By default it checks the package.json for any listed ones, but subclasses
can override this method to do it a different way.

@property processManagers
@type Object
@public