title: How to use proxy for R?
body: <p>I want to use google api, but in some country like China
  we are not free to connect google, especially in R using API
  so we need a way to do that </p>
  
  <p>after several hours try, I finally could make it.
  In order to help others go through the hardest part</p>
  
  <p>I will post my answer below</p>