Fix [typos]: performance-tips.md (#110)

docs/guides/production/performance-tips.md

@@ -42,7 +42,7 @@
 - Masks can be expensive if too many are used: e.g., 100s of masks will really slow things down
 - Axis-aligned Rectangle masks are the fastest (as the use scissor rect)
 - Graphics masks are second fastest (as they use the stencil buffer)
-- Sprite masks are the third fastest (they uses filters). They are really expensive. Do not use too many in your scene!
+- Sprite masks are the third fastest (they use filters). They are really expensive. Do not use too many in your scene!
 
 ### Filters