fix trailing whitespace

this commit got dropped during landing

modules/encoders/x64/xor.rb

@@ -24,11 +24,10 @@ class MetasploitModule < Msf::Encoder::Xor
         }
       )
   end
-  
   # Indicate that this module can preserve some registers
   # ...which is currently not true. This is a temp fix
   # until the full preserve_registers functionality is
-  # implemented. 
+  # implemented.
   def can_preserve_registers?
     true
   end