Fix syntax error in comment code

Closing parentheses is missing in the example code.

Author: Nirma

stdlib/public/core/StringInterpolation.swift

@@ -47,7 +47,7 @@
 ///         fileprivate mutating func appendInterpolation(
 ///                  escaped value: String, asASCII forceASCII: Bool = false) {
 ///             for char in value.unicodeScalars {
-///                 appendInterpolation(char.escaped(asASCII: forceASCII)
+///                 appendInterpolation(char.escaped(asASCII: forceASCII))
 ///             }
 ///         }
 ///     }