Added error handling to filestream

This would have probably rejected the promise anyway because uncaught
error, but it's better to be explicit

ghost/release-utils/lib/releases.js

@@ -108,6 +108,7 @@ module.exports.uploadZip = (options = {}) => {
 
     return new Promise((resolve, reject) => {
         fs.createReadStream(options.zipPath)
+            .on('error', reject)
             .pipe(request.post(reqOptions, (err, res) => {
                 if (err) {
                     return reject(err);