modify sdk version

Author: qinhui

iOS/APIExample/Podfile

@@ -4,7 +4,7 @@
 #source 'https://mirrors.tuna.tsinghua.edu.cn/git/CocoaPods/Specs.git'
 
 def common_pods
-  #  pod 'AgoraRtcEngine_iOS', '4.6.2'
+  #  pod 'AgoraRtcEngine_iOS', '4.5.3'
    pod 'sdk', :path => 'sdk.podspec'
 end