Fixed the following golint warnigns:
 - package_validator.go:68:1: receiver name should not be an underscore, omit the name if it is unused
 - package_validator.go:89:1: receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"
 - package_validator.go:96:1: receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"
 - package_validator.go:119:1: receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"