make entry even faster.

index.html

@@ -61,7 +61,13 @@ cuberoot.addEventListener("keydown", function (e) {
   if (e.keyCode === 13) {
     check_cuberoot(e);
   }
-})
+});
+
+cuberoot.addEventListener("keyup", function (e) {
+  if (cuberoot.value.length >= 2) {
+    check_cuberoot(e);
+  }
+});
 
 function humanize_ms(ms) {
   if (ms < 1000) {