2.8.0 readiness

- Updates branch aliases
  - dev-master => 2.8.x-dev
  - dev-develop => 2.9.x-dev
- Updates CHANGELOG
  - Combines 2.7.2 and 2.8.0 entries
  - Sets release date for 2.8.0

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 All notable changes to this project will be documented in this file, in reverse chronological order by release.
 
-## 2.8.0 - TBD
+## 2.8.0 - 2019-12-26
 
 ### Added
 
@@ -14,28 +14,6 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Deprecated
 
-- Nothing.
-
-### Removed
-
-- Nothing.
-
-### Fixed
-
-- Nothing.
-
-## 2.7.2 - TBD
-
-### Added
-
-- Nothing.
-
-### Changed
-
-- Nothing.
-
-### Deprecated
-
 - [#49](https://github.com/zendframework/zend-barcode/pull/49) deprecates `Zend\Barcode\Renderer\Pdf`. The renderer uses the now-abandoned zendframework/zendpdf package, and, as such, is deprecated as well, and scheduled for removal with version 3.0.0. We will release a separate PDF renderer package at a later date that consumes a 3rd party PDF library.
 
 ### Removed

composer.json

@@ -45,8 +45,8 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.7.x-dev",
-            "dev-develop": "2.8.x-dev"
+            "dev-master": "2.8.x-dev",
+            "dev-develop": "2.9.x-dev"
         }
     },
     "scripts": {