add audit for Formula.factory

Library/Homebrew/cmd/audit.rb

@@ -180,7 +180,7 @@ class FormulaAuditor
   def audit_conflicts
     f.conflicts.each do |c|
       begin
-        Formula.factory(c.name)
+        Formulary.factory(c.name)
       rescue FormulaUnavailableError
         problem "Can't find conflicting formula #{c.name.inspect}."
       end
@@ -299,6 +299,10 @@ class FormulaAuditor
     if text =~ /system\s+['"]xcodebuild/ && text !~ /SYMROOT=/
       problem "xcodebuild should be passed an explicit \"SYMROOT\""
     end
+
+    if text =~ /Formula\.factory\(/
+      problem "\"Formula.factory(name)\" is deprecated in favor of \"Formula[name]\""
+    end
   end
 
   def audit_line(line)