Stream lines using setImmediate to ensure it doesn't block event loop

lib/storage.js

@@ -89,14 +89,18 @@ storage.crashSafeWriteFileLines = (filename, lines, callback = () => {}) => {
     },
     cb => {
       try {
-        const stream = fs.createWriteStream(tempFilename, {
-          flags: 'w'
-        })
-        for (const line of lines) {
-          stream.write(line)
-          stream.write('\n')
+        const stream = fs.createWriteStream(tempFilename)
+        const next = () => {
+          const line = lines.shift()
+          if (line === undefined) {
+            stream.close(cb)
+          } else {
+            stream.write(line)
+            stream.write('\n')
+            setImmediate(next)
+          }
         }
-        stream.close(() => cb())
+        next()
       } catch (err) {
         cb(err)
       }