Update README.md (#631)

Changes proposed in this pull request:
- Fix typo in readme

README.md

@@ -153,7 +153,7 @@ or for newest version from specified branch of code:
 pod 'CryptoSwift', :git => "https://github.com/krzyzanowskim/CryptoSwift", :branch => "master"
 ```
 
-Bear in mind that CocoaPods will build CryptoSwift without [Whole-Module Optimization](https://swift.org/blog/whole-module-optimizations/) that my impact performance. You can change it manually after installation, or use [cocoapods-wholemodule](https://github.com/jedlewison/cocoapods-wholemodule) plugin.
+Bear in mind that CocoaPods will build CryptoSwift without [Whole-Module Optimization](https://swift.org/blog/whole-module-optimizations/) that may impact performance. You can change it manually after installation, or use [cocoapods-wholemodule](https://github.com/jedlewison/cocoapods-wholemodule) plugin.
 
 #### Carthage 
 You can use [Carthage](https://github.com/Carthage/Carthage).