Apply even more let/const transforms.

endsWith.js

@@ -30,12 +30,12 @@ function endsWith(string, target, position) {
   string = toString(string);
   target = baseToString(target);
 
-  var length = string.length;
+  const length = string.length;
   position = position === undefined
     ? length
     : baseClamp(toInteger(position), 0, length);
 
-  var end = position;
+  const end = position;
   position -= target.length;
   return position >= 0 && string.slice(position, end) == target;
 }