[css-images] tpyo. Fixes w3c#1769.

Author: tabatkins

css-images/Overview.bs

@@ -1503,8 +1503,8 @@ Image Processing {#image-processing}
 ████ ██     ██ ██     ██  ██████   ████████         ██     ██ ████████ ██    ██ ████████  ████████ ██     ██ ████ ██    ██  ██████
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-Determing How To Scale an Image: the 'image-rendering' property {#the-image-rendering}
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+Determining How To Scale an Image: the 'image-rendering' property {#the-image-rendering}
+----------------------------------------------------------------------------------------
 
 	<pre class='propdef'>
 	Name: image-rendering