Fix a lifetime bug uncovered by NLL, thanks @lqd

A similar error message was: https://play.rust-lang.org/?gist=4c5f4002623da9a3df723c9540dd125e&version=nightly&mode=debug&edition=2015

```rust
error[E0509]: cannot move out of type `S<'_>`, which implements the `Drop` trait
  --> src/main.rs:15:17
   |
15 |         let S { url } = self;
   |                 ^^^ cannot move out of here
```

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