Fixes quotes

Previous ones were not recognized as valid characters by Carthage

Author: michalkalinowski-

README.md

@@ -39,7 +39,7 @@ $ open MyProject.xcworkspace
 If you are using Carthage you will need to add this to your `Cartfile`
 
 ```bash
-github “jpotts18/SwiftValidator”
+github "jpotts18/SwiftValidator"
 ```
 
 ## Usage