Update README.md

subjects/interpolation/README.md

@@ -5,7 +5,7 @@
 Create a function called `interpolation` that takes an object with 5 properties
 `step`, `start`, `end`, `callback` and `duration`.
 This function must calculate the interpolation points, (x, y),
-from the `start` position to `end` position depending on the number of `step`s.
+from the `start` position to `end` position depending on the number of steps.
 All the points must be calculated in the duration time.
 
 For each interpolation point you must call `callback` function with parameter - interpolation point ([x, y]).