clippy: fix unwrap_or followed by new

```
src/main.rs:139:18: 139:73 warning: use of `unwrap_or` followed by a call to `new`, #[warn(or_fun_call)] on by default
src/main.rs:139         configs: matches.values_of_lossy("config").unwrap_or(Vec::new()),
                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/main.rs:139:18: 139:73 help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#or_fun_call
src/main.rs:139:18: 139:73 help: try this
src/main.rs:            configs: matches.values_of_lossy("config").unwrap_or_default(),
```

Signed-off-by: Paul Osborne <[email protected]>

Author: posborne

src/main.rs

@@ -136,7 +136,7 @@ fn main() {
 
     // process global options
     let gpio_options = GpioOptions {
-        configs: matches.values_of_lossy("config").unwrap_or(Vec::new()),
+        configs: matches.values_of_lossy("config").unwrap_or_default(),
     };
 
     // parse the config