Fix some typos in Date.swift (#448)

Author: KentaKudo

Foundation/Date.swift

@@ -90,7 +90,7 @@ public struct Date : ReferenceConvertible, Comparable, Equatable, CustomStringCo
     /**
      The time interval between the date and the current date and time.
 
-     If the date is earlier than the current date and time, the this property’s value is negative.
+     If the date is earlier than the current date and time, this property’s value is negative.
 
      - SeeAlso: `timeIntervalSince(_:)`
      - SeeAlso: `timeIntervalSince1970`
@@ -160,9 +160,9 @@ public struct Date : ReferenceConvertible, Comparable, Equatable, CustomStringCo
 
      - Parameter locale: A `Locale` object. If you pass `nil`, `NSDate` formats the date in the same way as the `description` property.
 
-     - Returns: A string representation of the receiver, using the given locale, or if the locale argument is `nil`, in the international format `YYYY-MM-DD HH:MM:SS ±HHMM`, where `±HHMM` represents the time zone offset in hours and minutes from UTC (for example, “`2001-03-24 10:45:32 +0600`”)
+     - Returns: A string representation of the receiver, using the given locale, or if the locale argument is `nil`, in the international format `YYYY-MM-DD HH:MM:SS ±HHMM`, where `±HHMM` represents the time zone offset in hours and minutes from UTC (for example, “`2001-03-24 10:45:32 +0600`”).
      */
-    public func description(with locale : Locale?) -> String {
+    public func description(with locale: Locale?) -> String {
         return NSDate(timeIntervalSinceReferenceDate: _time).descriptionWithLocale(locale)
     }