Add warnings to MessageInputBar

MessageKit.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
    s.name = 'MessageKit'
-   s.version = '3.0.0'
+   s.version = '3.0.0-beta'
    s.license = { :type => "MIT", :file => "LICENSE.md" }
 
    s.summary = 'An elegant messages UI library for iOS.'
@@ -15,6 +15,8 @@ Pod::Spec.new do |s|
       "SWIFT_VERSION" => "4.2",
    }
 
+   s.swift_version = '4.2'
+
    s.ios.deployment_target = '9.0'
    s.ios.resource_bundle = { 'MessageKitAssets' => 'Assets/MessageKitAssets.bundle/Images' }