updated REFERENCE.md to fix typo and clarify key attribute

Author: taikaa

REFERENCE.md

@@ -182,8 +182,8 @@ specified as an array.
 
 ##### `key`
 
-The key itself; generally a long string of uuencoded characters. The `key`
-attribute may not contain whitespace.
+The key itself; generally a long string of unencoded characters. The `key`
+attribute may not contain leading or trailing whitespace.
 
 Make sure to omit the following in this attribute (and specify them in
 other attributes):