fix travis error, hopefully

browser/fs.js

@@ -1,13 +1,5 @@
-export function readdirSync () {
-	throw new Error( 'Cannot use fs.readdirSync inside browser' );
-}
+const nope = method => `Cannot use fs.${method} inside browser`;
 
-export function readFileSync () {
-	throw new Error( 'Cannot use fs.readFileSync inside browser' );
-}
-
-export function writeFile () {
-	throw new Error( 'Cannot use fs.writeFile inside browser' );
-}
-
-export const Promise = window.Promise;
+export const readdirSync = nope( 'readdirSync' );
+export const readFileSync = nope( 'readFileSync' );
+export const writeFile = nope( 'writeFile' );

src/utils/fs.js

@@ -1,9 +1,10 @@
 import Promise from 'es6-promise/lib/es6-promise/promise';
 import * as fs from 'fs';
+import { resolve } from './path';
 
 export function writeFile ( dest, data ) {
 	return new Promise( ( fulfil, reject ) => {
-		fs.writeFile( dest, data, err => {
+		fs.writeFile( resolve( process.cwd(), dest ), data, err => {
 			if ( err ) {
 				reject( err );
 			} else {