fix: a typo

Author: f-frhs

src/Spatial/Euclidean/Circle2D.cs

@@ -154,13 +154,13 @@ private double[] findParameterTs(Line2D line)
             // (p-cc)^2=r^2 (eq1)
             // p=s+t*d     (eq2)
             // , where p is the point on the line and/or circle,
-            // c is the center of the circle,
+            // cc is the center of the circle,
             // r is the radius of the circle,
             // s is the starting point of the line,
             // t is the parameter and
             // d is the line direction.
             // Substituting (eq2) into (eq1) yields:
-            // ((s+t*d)-c)^2=r^2 (eq3)
+            // ((s+t*d)-cc)^2=r^2 (eq3)
             // (eq3) reduces to the following quadratic equation: a*t^2 + b*t + c==0
 
             var cc = this.Center.ToVector2D(); //center of circle