Clarify code comment for StripAttribute

It could be misleading to say it's cleaning the attribute,
as it's not performing any sanitization.

app/models/concerns/strip_attribute.rb

@@ -2,7 +2,8 @@
 
 # == Strip Attribute module
 #
-# Contains functionality to clean attributes before validation
+# Contains functionality to remove leading and trailing
+# whitespace from the attribute before validation
 #
 # Usage:
 #