[PodTargetInstaller] Set deployment target to maximum spec deployment target

lib/cocoapods/installer/target_installer.rb

@@ -39,7 +39,6 @@ module Pod
         product_type = target.product_type
         name = target.label
         platform = target.platform.name
-        deployment_target = target.platform.deployment_target.to_s
         language = target.uses_swift? ? :swift : :objc
         @native_target = project.new_target(product_type, name, platform, deployment_target, nil, language)
 
@@ -59,6 +58,12 @@ module Pod
         target.native_target = @native_target
       end
 
+      # @return [String] The deployment target.
+      #
+      def deployment_target
+        target.platform.deployment_target.to_s
+      end
+
       # Returns the customized build settings which are overridden in the build
       # settings of the user target.
       #

lib/cocoapods/installer/target_installer/pod_target_installer.rb

@@ -310,6 +310,15 @@ module Pod
         end
       end
 
+      # The deployment target for the pod target, which is the maximum of all
+      # the deployment targets for the current platform of the target.
+      #
+      # @return [String] The deployment target.
+      #
+      def deployment_target
+        target.specs.map { |spec| spec.deployment_target(target.platform) }.max
+      end
+
       #-----------------------------------------------------------------------#
     end
   end