roadmap.md: fix little typo

Author: ferhatgec

microsoft-edge/webview2/roadmap.md

@@ -18,7 +18,7 @@ If you have concerns or questions about the Roadmap, provide your feedback in th
 
 The WebView2 team is planning the following major efforts for future updates:
 
-* MacOS Preview
+* macOS Preview
 * Xbox Preview
 * Linux Preview