document why

Author: Brent Cook

metasploit-framework.gemspec

@@ -83,7 +83,9 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency 'packetfu'
   # For sniffer and raw socket modules
   spec.add_runtime_dependency 'pcaprub'
-  # Needed for module caching in Mdm::ModuleDetails
+  # Used by the Metasploit data model, etc.
+  # bound to 0.20 for Activerecord 4.2.8 deprecation warnings:
+  # https://github.com/ged/ruby-pg/commit/c90ac644e861857ae75638eb6954b1cb49617090
   spec.add_runtime_dependency 'pg', '0.20.0'
   # Run initializers for metasploit-concern, metasploit-credential, metasploit_data_models Rails::Engines
   spec.add_runtime_dependency 'railties'