[css-images-3] fix typo

Author: fantasai

css-images-3/Overview.bs

@@ -1839,7 +1839,7 @@ Determining How To Scale an Image: the 'image-rendering' property {#the-image-re
 
 		The ''pixelated'' version maintains the overall <em>look</em> of simply scaling the pixels up,
 		at the cost of <em>slight</em> blurring,
-		tho much less blurring than the ''smooth'' scaling gives.
+		though much less blurring than the ''smooth'' scaling gives.
 		Meanwhile, ''crisp-edges'' avoids introducing any blurring at all,
 		at the cost of aliasing artifacts
 		making the "pixels" look irregularly sized.