release: 2.8.0 readiness

- set release date in CHANGELOG.md
- remove empty stub in CHANGELOG.md
- update branch-alias section in composer.json
  - dev-master => 2.8.x-dev
  - dev-develop => 2.9.x-dev

Author: michalbundyra

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 - 2019-10-19
 
 ### Added
 
@@ -24,28 +24,6 @@ All notable changes to this project will be documented in this file, in reverse
 
 - Nothing.
 
-## 2.7.1 - TBD
-
-### Added
-
-- Nothing.
-
-### Changed
-
-- Nothing.
-
-### Deprecated
-
-- Nothing.
-
-### Removed
-
-- Nothing.
-
-### Fixed
-
-- Nothing.
-
 ## 2.7.0 - 2018-05-14
 
 ### Added

composer.json

@@ -49,8 +49,8 @@
     },
     "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": {