Do minor optimisations to factorial function.

Author: trekhleb

src/algorithms/math/factorial/factorial.js

@@ -5,7 +5,7 @@
 exportdefaultfunctionfactorial(number){
 letresult=1;
 
-for(leti=1;i<=number;i+=1){
+for(leti=2;i<=number;i+=1){
 result*=i;
 }