feat: pods use the same deployment target

CocoaMQTT.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name        = "CocoaMQTT"
-  s.version     = "2.1.4"
+  s.version     = "2.1.5"
   s.summary     = "MQTT v3.1.1 client library for iOS and OS X written with Swift 5"
   s.homepage    = "https://github.com/emqx/CocoaMQTT"
   s.license     = { :type => "MIT" }
@@ -12,7 +12,7 @@ Pod::Spec.new do |s|
   s.ios.deployment_target = "11.0"
   s.tvos.deployment_target = "10.0"
   # s.watchos.deployment_target = "2.0"
-  s.source   = { :git => "https://github.com/emqx/CocoaMQTT.git", :tag => "2.1.4"}
+  s.source   = { :git => "https://github.com/emqx/CocoaMQTT.git", :tag => "2.1.5"}
   s.default_subspec = 'Core'
 
   s.subspec 'Core' do |ss|

Example/Podfile

@@ -2,5 +2,12 @@ platform :ios, 11.0
 use_frameworks!
 
 target 'Example' do
+    post_install do |installer|
+        installer.pods_project.targets.each do |target|
+            target.build_configurations.each do |config|
+                config.build_settings.delete 'IPHONEOS_DEPLOYMENT_TARGET'
+            end
+        end
+    end    
     pod 'CocoaMQTT/WebSockets', :path => '../'
 end