print deprecation warning at runtime instead of during gem installation

Author: oreoshake

lib/secure_headers.rb

@@ -39,6 +39,9 @@ def secure_headers_options
     end
 
     def ensure_security_headers options = {}
+      if RUBY_VERSION == "1.8.7"
+        warn "[DEPRECATION] secure_headers ruby 1.8.7 support will dropped in the next release"
+      end
       self.secure_headers_options = options
       before_filter :prep_script_hash
       before_filter :set_hsts_header

secure_headers.gemspec

@@ -20,5 +20,4 @@ Gem::Specification.new do |gem|
   gem.require_paths = ["lib"]
   gem.add_development_dependency "rake"
   gem.add_dependency "user_agent_parser"
-  gem.post_install_message = "Heads up, secure_headers Ruby 1.8.7 support will go away in the next major release."
 end