release: 3.4.0 readiness

- set release date in CHANGELOG.md
- update branch-aliases in composer.json
  - dev-master => 3.4.x-dev
  - dev-develop => 3.5.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.
 
-## 3.4.0 - TBD
+## 3.4.0 - 2019-10-06
 
 ### Added
 

composer.json

@@ -45,8 +45,8 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "3.3.x-dev",
-            "dev-develop": "3.4.x-dev"
+            "dev-master": "3.4.x-dev",
+            "dev-develop": "3.5.x-dev"
         }
     },
     "scripts": {