Utilize Some/None return from slice::first()

src/lib.rs

@@ -1,11 +1,11 @@
 pub fn build_proverb(list: &[&str]) -> String {
     let mut verse = "".to_string();
 
-    if !list.is_empty() {
+    if let Some(nail) = list.first() {
         for item in list.windows(2) {
             verse.push_str(&format!("For want of a {} the {} was lost.\n", item[0], item[1]));
         }
-        verse.push_str(&format!("And all for the want of a {}.", list[0]));
+        verse.push_str(&format!("And all for the want of a {}.", nail));
     }
 
     verse