Fix typo in README documentation.

Author: natestedman

README.md

@@ -63,7 +63,7 @@ These additional framework types are extended with attribute functions:
 - `NSTextAttachment`: `attribute`, which maps to `NSAttachmentAttributeName`.
 - `NSParagraphStyle`: `attribute`, which maps to `NSParagraphStyleAttributeName`.
 - `NSShadow`: `attribute`, which maps to `NSShadowAttributeName`.
-- `NSUnderlineStyle`: `attribute`, which maps to `NSUnderlineStyleAttributeName`; and `strikethroughAttribute`, which makes to `NSStrikethroughStyleAttributeName`.
+- `NSUnderlineStyle`: `attribute`, which maps to `NSUnderlineStyleAttributeName`; and `strikethroughAttribute`, which maps to `NSStrikethroughStyleAttributeName`.
 - `String`, on OS X only: `toolTipAttribute`, which maps to `NSToolTipAttributeName`.
 
 #### Numeric Types