title: How to find the next greater string in alphabetical order in Golang?
body: <p>eg: abc<strong>d</strong> -> abc<strong>e</strong> ,  qwe<strong>r</strong> -> qwe<strong>s</strong> etc</p>
  
  <p>my_string := "abcd"</p>
  
  <p>How can I get my_string to have "abce" ?</p>