Fix readme example (#62)

Remove undefined `resolve` function from example

README.md

@@ -146,7 +146,7 @@ const axiosInstance = axios.create({ baseURL: BASE_URL })
 const requestRefresh = (refresh) => {
     // Notice that this is the global axios instance, not the axiosInstance!  <-- important
     return axios.post(`${BASE_URL}/auth/refresh_token`, { refresh })
-      .then(response => resolve(response.data.access_token))
+      .then(response => response.data.access_token)
 };
 
 // 3. Apply interceptor