Add SE-0186 to changelog.

Author: gspiers

CHANGELOG.md

@@ -22,6 +22,21 @@ CHANGELOG
 Swift 4.1
 ---------
 
+* [SE-0186][]
+
+  It is no longer valid to use the ownership keywords `weak` and `unowned` for property declarations in protocols. These keywords are meaningless and misleading when used in a protocol as they don't have any effect.
+
+  In Swift 3 and 4 mode the following example will produce a warning with a fix-it to remove the keyword. In Swift 5 mode and above an error will be produced.
+
+  ```swift
+  class A {}
+
+  protocol P {
+      weak var weakVar: A? { get set }
+      unowned var unownedVar: A { get set }
+  }
+  ```
+
 * [SE-0185][]
 
   Structs and enums that declare a conformance to `Equatable`/`Hashable` now get an automatically synthesized implementation of `==`/`hashValue`. For structs, all stored properties must be `Equatable`/`Hashable`. For enums, all enum cases with associated values must be `Equatable`/`Hashable`.
@@ -6754,3 +6769,4 @@ Swift 1.0
 [SE-0183]: <https://github.com/apple/swift-evolution/blob/master/proposals/0183-substring-affordances.md>
 [SE-0184]: <https://github.com/apple/swift-evolution/blob/master/proposals/0184-unsafe-pointers-add-missing.md>
 [SE-0185]: <https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.md>
+[SE-0186]: <https://github.com/apple/swift-evolution/blob/master/proposals/0186-remove-ownership-keyword-support-in-protocols.md>