Update CHANGELOG for v1.7.3 (#176)

* Update CHANGELOG.md

* Add links for CHANGELOG

CHANGELOG.md

@@ -7,6 +7,11 @@ Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+## [1.7.3] - 2018-06-30
+### Fixed
+- Merge PR #174, fixing validation support for AWS::URLSuffix
+- Merge PR #171, fixing support for Fn::ImportValue to Fn::Split intrinsic function
+
 ## [1.7.2] - 2018-06-02
 ### Changed
 - Merge PR #162, add release instructions to README.md
@@ -145,7 +150,8 @@ Versioning](http://semver.org/spec/v2.0.0.html).
 ### Added
 - Add pseudo parameter support
 
-[Unreleased]: https://github.com/martysweet/cfn-lint/compare/v1.7.2...HEAD
+[Unreleased]: https://github.com/martysweet/cfn-lint/compare/v1.7.3...HEAD
+[1.7.3]: https://github.com/martysweet/cfn-lint/compare/v1.7.2...v1.7.3
 [1.7.2]: https://github.com/martysweet/cfn-lint/compare/v1.7.1...v1.7.2
 [1.7.1]: https://github.com/martysweet/cfn-lint/compare/v1.7.0...v1.7.1
 [1.7.0]: https://github.com/martysweet/cfn-lint/compare/v1.6.2...v1.7.0