title: Error when trying to modify URL path in R API package
body: <p>I am writing my first R API package and am following Hadley Wickham's Best Practices Guide for API Packages and have hit a snag. The base URL for the API is <a href="https://journaltransfer.issn.org/api?query=" rel="nofollow noreferrer">https://journaltransfer.issn.org/api?query=</a>. The problem I am facing is that when I attempt to modify the url, the query isn't appended to the end after the = sign, but instead replaces the word api. How do I fix this issue?</p>
  
  <pre><code>library(httr)
  
  rtransfers &lt;- function(path) {
    url &lt;- modify_url("https://journaltransfer.issn.org/api?query=", path = path)
    GET(url)
  }
  
  resp &lt;- rtransfers("*")
  </code></pre>
  
  <p>I expect the url that would have been run by <code>rtransfers</code> to be: <a href="https://journaltransfer.issn.org/api?query=" rel="nofollow noreferrer">https://journaltransfer.issn.org/api?query=</a>* but instead it ends up being <a href="https://journaltransfer.issn.org/" rel="nofollow noreferrer">https://journaltransfer.issn.org/</a>*?query=</p>