fix(xo-server/_parseDuration): add missing file

Related to 6baef2450

packages/xo-server/src/_parseDuration.js

@@ -0,0 +1,12 @@
+import ms from 'ms'
+
+export default value => {
+  if (typeof value === 'number') {
+    return value
+  }
+  const duration = ms(value)
+  if (duration === undefined) {
+    throw new TypeError(`not a valid duration: ${duration}`)
+  }
+  return duration
+}