throw an error when starting vault if one occurs (#6235)

* throw an error when starting vault if one occurs

* use node 10

* do not use shorthand

.travis.yml

@@ -27,8 +27,8 @@ cache:
   - ui/node_modules
 
 before_install:
-  - nvm install 8
-  - nvm use 8
+  - nvm install 10
+  - nvm use 10
   - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.12.1
   - export PATH="$HOME/.yarn/bin:$PATH"
 

ui/scripts/start-vault.js

@@ -42,7 +42,10 @@ readline
     if (root && unseal) {
       fs.writeFile(
         path.join(process.cwd(), 'tests/helpers/vault-keys.js'),
-        `export default ${JSON.stringify({ unseal, root }, null, 2)}`
+        `export default ${JSON.stringify({ unseal, root }, null, 2)}`,
+        err => {
+          if (err) throw err;
+        }
       );
 
       console.log('VAULT SERVER READY');
@@ -71,7 +74,7 @@ process.on('exit', function() {
   vault.kill('SIGINT');
 });
 
-fs.writeFile(pidFile, process.pid, (err) => {
+fs.writeFile(pidFile, process.pid, err => {
   if (err) throw err;
   console.log('The file has been saved!');
 });