Fix carthage setting of readme

YamatoOtaka · freak4pc · commit a4030e38380a · 2020-10-26T19:28:29.000+02:00
diff --git a/README.md b/README.md
@@ -170,7 +170,7 @@ Officially supported: Carthage 0.33 and up.
 Add this to `Cartfile`
 
 ```
-github "ReactiveX/RxSwift" '6.0.0-rc.1'
+github "ReactiveX/RxSwift" "6.0.0-rc.1"
 ```
 
 ```bash
