[editorial] convert example to use single instead of double quotes

Author: Mustafa UZUN

README.md

@@ -3131,7 +3131,7 @@ Other Style Guides
     });
 
     // good
-    const reaction = "No! That’s impossible!";
+    const reaction = 'No! That’s impossible!';
     (async function meanwhileOnTheFalcon() {
       // handle `leia`, `lando`, `chewie`, `r2`, `c3p0`
       // ...