replace const with let and write single line comment correctly

Author: Dipa-Sarker

Sprint-1/2-mandatory-errors/1.js

@@ -1,6 +1,6 @@
 
-const age = 33;
+let age = 33;
 age = age + 1;
 
-// There is a constant variable age, which is fixed and it's value cannot be reassigned.//
-// If we want to change the value of age, we have to use let instead of const. //
+// There is a constant variable age, which is fixed and it's value cannot be reassigned.
+// If we want to change the value of age, we have to use let instead of const.