Land rapid7#4720, update Rails 3-style .find(:first)

Eliminate the Rails 3-style .find(:first) calls, and replace with
Rails 4-compatible .first().

Fixes rapid7#4720, also see MSP-12012

Author: mbuck-r7

lib/msf/core/db_manager.rb

@@ -130,7 +130,7 @@ def initialize(framework, opts = {})
   #
   def check
   ::ActiveRecord::Base.connection_pool.with_connection {
-    res = ::Mdm::Host.find(:first)
+    res = ::Mdm::Host.first
   }
   end
 

lib/msf/core/db_manager/vuln.rb

@@ -31,15 +31,15 @@ def find_vuln_by_details(details_map, host, service=nil)
     vuln = nil
 
     if service
-      vuln = service.vulns.find(:first, :include => [:vuln_details], :conditions => crit)
+      vuln = service.vulns.includes(:vuln_details).where(:crit).first
     end
 
     # Return if we matched based on service
     return vuln if vuln
 
     # Prevent matches against other services
     crit["vulns.service_id"] = nil if service
-    vuln = host.vulns.find(:first, :include => [:vuln_details], :conditions => crit)
+    vuln = host.vulns.includes(:vuln_details).where(:crit).first
 
     return vuln
   end