【Vue.jsエラー】Error in created hook: "ReferenceError: axios is not defined"

app.js:13672 [Vue warn]: Error in created hook: "ReferenceError: axios is not defined"

...

app.js:14935 ReferenceError: axios is not defined
    at VueComponent.getChannels (app.js:955)
    at VueComponent.created (app.js:943)
    at invokeWithErrorHandling (app.js:14901)
    at callHook (app.js:17252)
    at VueComponent.Vue._init (app.js:18034)
    at new VueComponent (app.js:18179)
    at createComponentInstanceForVnode (app.js:16328)
    at init (app.js:16159)
    at merged (app.js:16346)
    at createComponent (app.js:19005)

require('./bootstrap');