Implement variant on version to require catch-all (#159)

src/version.rs

@@ -49,6 +49,7 @@ enum Http {
     Http11,
     H2,
     H3,
+    __NonExhaustive,
 }
 
 impl Default for Version {
@@ -68,6 +69,7 @@ impl fmt::Debug for Version {
             Http11 => "HTTP/1.1",
             H2     => "HTTP/2.0",
             H3     => "HTTP/3.0",
+            __NonExhaustive => unreachable!(),
         })
     }
 }