Update podspec and README to version 2.2.0

Amplitude-iOS.podspec

@@ -1,11 +1,11 @@
 Pod::Spec.new do |s|
   s.name         = "Amplitude-iOS"
-  s.version      = "2.1.1"
+  s.version      = "2.2.0"
   s.summary      = "Amplitude mobile analytics iOS SDK."
   s.homepage     = "https://amplitude.com"
   s.license      = { :type => "MIT" }
   s.author       = { "Amplitude" => "dev@amplitude.com" }
-  s.source       = { :git => "https://github.com/amplitude/Amplitude-iOS.git", :tag => "v2.1.1" }
+  s.source       = { :git => "https://github.com/amplitude/Amplitude-iOS.git", :tag => "v2.2.0" }
   s.platform     = :ios, '5.0'
   s.source_files = '*.{h,m}'
   s.requires_arc = true

README.md

@@ -1,6 +1,6 @@
 # Setup #
 1. If you haven't already, go to https://amplitude.com and register for an account. You will receive an API Key.
-2. [Download the source code](https://github.com/amplitude/Amplitude-iOS/archive/master.zip) and extract the zip file. Alternatively, you can pull directly from GitHub. If you use Cocoapods, add the following line to your Podfile: `pod 'Amplitude-iOS', '~> 2.1'`
+2. [Download the source code](https://github.com/amplitude/Amplitude-iOS/archive/master.zip) and extract the zip file. Alternatively, you can pull directly from GitHub. If you use Cocoapods, add the following line to your Podfile: `pod 'Amplitude-iOS', '~> 2.2'`
 3. Copy the Amplitude-iOS folder into the source of your project in XCode. Check "Copy items into destination group's folder (if needed)".
 
 4. In every file that uses analytics, import Amplitude.h at the top: