Land rapid7#2702, uninit const fix for HttpClient

Author: wvu

lib/msf/core/exploit/http/client.rb

@@ -126,7 +126,7 @@ def validate_fingerprint()
         opts[:pattern].each do |re|
           if not re.match(info)
             err = "The target server fingerprint \"#{info}\" does not match \"#{re.to_s}\", use 'set FingerprintCheck false' to disable this check."
-            fail_with(Failure::NotFound, err)
+            fail_with(::Msf::Module::Failure::NotFound, err)
           end
         end
       end