code: function installMissing( error, collected ) {
  	if ( error ) {
  		console.error( `checking dependencies failed: ${error.message}` );
  
  		process.exit( 1 );
  		return;
  	}
  
  	if ( collected.length < 1 ) {
  		postProcess( 0 );
  	} else {
  		if ( !quiet ) {
  			console.error( `installing missing dependencies:\n${collected.map( d => `* ${d}`).join( "\n" )}` );
  		}
  
  		const npm = Child.exec( `npm install --no-save ${collected.join( " " )}`, {
  			stdio: "pipe",
  		} );
  
  		npm.stdout.pipe( process.stdout );
  		npm.stderr.pipe( process.stderr );
  
  		npm.on( "exit", postProcess );
  	}
  }
docs: Installs collected dependencies considered missing or handles provided error.
  
  @param {Error} error encountered error
  @param {string[]} collected list of dependencies considered missing