fix spelling in core libraries

sdk/lib/math/rectangle.dart

Index: sdk/lib/math/rectangle.dart
diff --git a/sdk/lib/math/rectangle.dart b/sdk/lib/math/rectangle.dart
index 2145cc739fb0758cae06befd326ece8d72fe23fe..66a2fc3a2afa7f64307674cee1039204778858b7 100644
--- a/sdk/lib/math/rectangle.dart
+++ b/sdk/lib/math/rectangle.dart
@@ -15,7 +15,7 @@ part of dart.math;
  *
  * The rectangle is the set of points with representable coordinates greater
  * than or equal to left/top, and with distance to left/top no greater than
- * width/height (to the limit of the precission of the coordinates).
+ * width/height (to the limit of the precision of the coordinates).
  */
 abstract class _RectangleBase<T extends num> {
   const _RectangleBase();