Update CHANGELOG.md

Author: tjcelaya

CHANGELOG.md

@@ -5,7 +5,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [4.0.8]
 
 ### Fixed
-- [NullPointerException when key file is not a valid private key]https://github.com/joyent/java-http-signature/issues/50
+- [NullPointerException when key file is not a valid private key](https://github.com/joyent/java-http-signature/issues/50)
 
 ## [4.0.7] - 2018-04-02