login: don't attempt json parsing if non-200

lib/login.js

@@ -28,6 +28,10 @@ async function getVerificationToken (email) {
     body: data
   });
 
+  if (200 !== res.status) {
+    throw new Error('Verification error');
+  }
+
   const body = await res.json();
   return body.token;
 }