Split off v5 branch to indicate BC for Laravel 5.7 and 5.8

Author: Ciaro

README.markdown

@@ -6,7 +6,8 @@
 
 This is a Laravel 4-5 package for working with trees in relational databases.
 
-*   **Laravel 5.5, 5.6, 5.7, 5.8** is supported since v4.3
+*   **Laravel 5.7, 5.8** is supported since v5
+*   **Laravel 5.5, 5.6** is supported since v4.3
 *   **Laravel 5.2, 5.3, 5.4** is supported since v4
 *   **Laravel 5.1** is supported in v3
 *   **Laravel 4** is supported in v2

composer.json

@@ -33,7 +33,7 @@
 
     "extra": {
         "branch-alias": {
-            "dev-master": "v4.2.x-dev"
+            "dev-master": "v5.0.x-dev"
         },
 
         "laravel": {