Fix default idiom example (#134)

Before this change, the example code doesn't run on the current rust stable release(1.49).
This is because `Path` inherently has a u8 that requires the sized trait which requires either statics or replacing Path with PathBuf.

After this change, the example code will run "as-is" without warnings or errors.

idioms/default.md

@@ -19,14 +19,16 @@ different names, but there can only be one `Default` implementation per type.
 
 ## Example
 
-```rust,ignore
+```rust
+use std::{path::PathBuf, time::Duration};
+
 // note that we can simply auto-derive Default here.
-#[derive(Default)]
+#[derive(Default, Debug)]
 struct MyConfiguration {
     // Option defaults to None
-    output: Option<Path>,
+    output: Option<PathBuf>,
     // Vecs default to empty vector
-    search_path: Vec<Path>,
+    search_path: Vec<PathBuf>,
     // Duration defaults to zero time
     timeout: Duration,
     // bool defaults to false
@@ -40,7 +42,9 @@ impl MyConfiguration {
 fn main() {
     // construct a new instance with default values
     let mut conf = MyConfiguration::default();
-    // do somthing with conf here
+    // do something with conf here
+    conf.check = true;
+    println!("conf = {:#?}", conf);
 }
 ```