Update 02_a_swift_tour.md

typo fixed.

source/chapter1/02_a_swift_tour.md

@@ -233,7 +233,7 @@ print(secondForLoop)
 func greet(name: String, day: String) -> String {
     return "Hello \(name), today is \(day)."
 }
-greet("Bob", "Tuesday")
+greet("Bob", day: "Tuesday")
 ```
 
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