feat: completed solutions

exercises/16_lifetimes/lifetimes1.rs

@@ -4,12 +4,8 @@
 // not own their own data. What if their owner goes out of scope?
 
 // TODO: Fix the compiler error by updating the function signature.
-fn longest(x: &str, y: &str) -> &str {
-    if x.len() > y.len() {
-        x
-    } else {
-        y
-    }
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+    if x.len() > y.len() { x } else { y }
 }
 
 fn main() {