clarify when we need to remove the xpath pin

Author: Brent Cook

metasploit-framework.gemspec

@@ -184,6 +184,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency 'nexpose'
   # Needed for NDMP sockets
   spec.add_runtime_dependency 'xdr'
-  # Needed for the xpath
+  # Needed to work around a regression between capybara 2.7.1 and xpath 2.1
+  # XXX remove when capybara is updated to work with xpath 2.1
   spec.add_runtime_dependency 'xpath', '2.0'
 end