[REFACTOR] [Hacker Rank] Interview Preparation Kit: Recursion: Davis' Staircase.

* Adjusted the interface to match what hackerrank expects.

Author: sir-gon

src/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_recursive_staircase.js

@@ -6,7 +6,7 @@
 const TOP_LIMIT = 10 ** 10 + 7;
 const STEPSLIMIT = 3;
 
-export class StepPerms {
+class StepPerms {
   TOP_LIMIT = 1;
 
   STEPS_LIMIT = 1;
@@ -39,10 +39,11 @@ export class StepPerms {
   }
 }
 
-export function stepPerms(n) {
+function stepPerms(n) {
   const stairs = new StepPerms(TOP_LIMIT, STEPSLIMIT);
 
   return stairs.stepPermsComputWithCache(n) % TOP_LIMIT;
 }
 
 export default { stepPerms, StepPerms };
+export { stepPerms, StepPerms };