[PodTarget] Clarify that subspecs across different build configs might come

lib/cocoapods/target/pod_target.rb

@@ -80,8 +80,8 @@ module Pod
       else
         raise Informative, "The subspecs of `#{pod_name}` are linked to " \
           "different build configurations for the `#{target_definition}` " \
-          'target. CocoaPods does not support subspecs across different ' \
-          'build configurations.'
+          'target. CocoaPods does not currently support subspecs across ' \
+          'different build configurations.'
       end
     end