Fix warning from Swift 4.2 compiler

Author: iwb-kevin-hirsch

DropDown.podspec

@@ -1,7 +1,7 @@
 Pod::Spec.new do |s|
 
   s.name = "DropDown"
-  s.version = "2.3.4"
+  s.version = "2.3.5"
   s.summary = "A Material Design drop down"
 
   s.description = <<-DESC

DropDown/src/DropDown.swift

@@ -722,7 +722,7 @@ extension DropDown {
 
 	fileprivate func fittingWidth() -> CGFloat {
 		if templateCell == nil {
-			templateCell = cellNib.instantiate(withOwner: nil, options: nil)[0] as! DropDownCell
+			templateCell = (cellNib.instantiate(withOwner: nil, options: nil)[0] as! DropDownCell)
 		}
 
 		var maxWidth: CGFloat = 0

README.md

@@ -2,7 +2,7 @@
 
 [![Twitter: @kevinh6113](http://img.shields.io/badge/contact-%40kevinh6113-70a1fb.svg?style=flat)](https://twitter.com/kevinh6113)
 [![License: MIT](http://img.shields.io/badge/license-MIT-70a1fb.svg?style=flat)](https://github.com/AssistoLab/DropDown/blob/master/README.md)
-[![Version](http://img.shields.io/badge/version-2.3.4-green.svg?style=flat)](https://github.com/AssistoLab/DropDown)
+[![Version](http://img.shields.io/badge/version-2.3.5-green.svg?style=flat)](https://github.com/AssistoLab/DropDown)
 [![Cocoapods](http://img.shields.io/badge/Cocoapods-available-green.svg?style=flat)](http://cocoadocs.org/docsets/DropDown/)
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
 
@@ -21,7 +21,7 @@ To install [CocoaPods](http://www.cocoapods.org), run `sudo gem install cocoapod
 
 ## Installation 📱
 
-`DropDown` supports Swift 4.2. 
+`DropDown` supports Swift 4.2 since version `2.3.4`.
 
 If you need Swift 4.0, use version 2.3.3:
 - Manually: use tag `2.3.3`