Fixed small typo

Author: ramadis

exercises/darts/description.md

@@ -10,6 +10,6 @@ In our particular instance of the game, the target rewards with 4 different amou
 * If the dart lands in the middle circle of the target, player earns 5 points.
 * If the dart lands in the inner circle of the target, player earns 10 points.
 
-The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are [concentrics](http://mathworld.wolfram.com/ConcentricCircles.html)).
+The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are [concentric](http://mathworld.wolfram.com/ConcentricCircles.html)).
 
 Write a function that given a point in the target (defined by its `real` cartesian coordinates `x` and `y`), returns the correct amount earned by a dart landing in that point.