In Swift 3 how to apply uppercase to only the first letter of a string?

Question

var bookTitle = "god of the forest"
bookTitle.uppercased()  // "GOD OF THE FOREST"
bookTitle.lowercased()  // "god of the forest"
bookTitle.capitalized   // doesn't work 

I get this error:

Value of type 'String' has no member 'capitalized'

I want the string to be like this:

"God Of The Forest"