refactor(youch): add conditional before looping over frames

frames can be undefined at times, so it is required to make sure frames is a valid array before

mapping over them

src/Youch/index.js

@@ -129,7 +129,7 @@ class Youch {
       message: this.error.message,
       name: this.error.name,
       status: this.error.status,
-      frames: stack.frames.map(callback)
+      frames: stack.frames instanceof Array === true ? stack.frames.map(callback) : []
     }
   }