title: Why is ": String" added onto rust let statement
body: <p>When I try to type:</p>
  <p><code>let mut guess = String::new();</code></p>
  <p>It changes to:</p>
  <p><code>let mut guess: String = String::new();</code></p>
  <p>I am using VScode, why is this happening?</p>