[PR #2104] Fixed misspelled words throughout the README.

CHANGELOG.md

@@ -743,7 +743,7 @@ Released on 2016-03-23. All issues associated with this milestone can be found u
   [#1099](https://github.com/Alamofire/Alamofire/pull/1099).
 
 #### Updated
-- The `User-Agent` header implementation to use more aggresive type-safety checks.
+- The `User-Agent` header implementation to use more aggressive type-safety checks.
   - Updated by [Christian Noon](https://github.com/cnoon) in regards to Issue
   [#1100](https://github.com/Alamofire/Alamofire/issues/1100).
 - All shared response serializers to accept a custom queue for execution.

Documentation/Alamofire 4.0 Migration Guide.md

@@ -699,7 +699,7 @@ Alamofire.download(urlString).responseData { response in
 }
 ```
 
-> We'll cover the `DownloadResponse` type in more detail in the [Reponse Serializers](#response-serializers) section.
+> We'll cover the `DownloadResponse` type in more detail in the [Response Serializers](#response-serializers) section.
 
 #### Download Options
 

Source/Request.swift

@@ -46,7 +46,7 @@ public typealias RequestRetryCompletion = (_ shouldRetry: Bool, _ timeDelay: Tim
 public protocol RequestRetrier {
     /// Determines whether the `Request` should be retried by calling the `completion` closure.
     ///
-    /// This operation is fully asychronous. Any amount of time can be taken to determine whether the request needs
+    /// This operation is fully asynchronous. Any amount of time can be taken to determine whether the request needs
     /// to be retried. The one requirement is that the completion closure is called to ensure the request is properly
     /// cleaned up after.
     ///