Rollup merge of rust-lang#25112 - jsyeo:jsyeo-while-let, r=alexcrichton

The indentation in this example is messed up. The `_ => break,` line was using a tab instead of spaces to indent.

Author: steveklabnik

src/doc/trpl/if-let.md

@@ -65,7 +65,7 @@ loop as long as a value matches a certain pattern. It turns code like this:
 loop {
     match option {
         Some(x) => println!("{}", x),
-	_ => break,
+        _ => break,
     }
 }
 ```