fix: replace stringify

stringify causes removal of functions on the object.
We work around this with serialize

lib/plugin.js

@@ -1,7 +1,7 @@
 import Vue from 'vue'
 import bugsnag from '@bugsnag/js'
 import bugsnagVue from '@bugsnag/plugin-vue'
-const bugsnagClient = bugsnag(<%= JSON.stringify(options) %>)
+const bugsnagClient = bugsnag(<%= serialize(options) %>)
 bugsnagClient.use(bugsnagVue, Vue)
 
 export default function ({ app }, inject) {