SHA-2 type is not "base64": better a string of 64 hexits (SHA-256).
Trivial case typo: "integer" => "Integer".
Merge pull request #360 from scara/Attachments_SHA2_Type_Should_Be_String_Not_Base64

SHA-2 type is not "base64": better a string of 64 (SHA-256) hex digits (hexits).