Implement BMI calculation function

Author: mrafeie

Sprint-3/3-mandatory-implement/1-bmi.js

@@ -16,4 +16,6 @@
 
 function calculateBMI(weight, height) {
   // return the BMI of someone based off their weight and height
+  const bmi = weight / (height * height);
+  return bmi.toFixed(1);
 }