Move website config to default branch

Adapts the website config to be compatible with the doctrine/doctrine-website#356 changes

Author: SenseException

.doctrine-project.json

@@ -4,21 +4,27 @@
     "slug": "coding-standard",
     "docsSlug": "doctrine-coding-standard",
     "versions": [
+        {
+            "name": "8.1",
+            "branchName": "8.1.x",
+            "slug": "8.1",
+            "current": true,
+            "aliases": [
+                "current",
+                "stable"
+            ]
+        },
         {
             "name": "8.0",
-            "branchName": "master",
-            "slug": "latest",
-            "upcoming": true
+            "branchName": "8.0.x",
+            "slug": "8.0",
+            "maintained": false
         },
         {
             "name": "7.0",
             "branchName": "7.0.x",
             "slug": "7.0",
-            "current": true,
-            "aliases": [
-                "current",
-                "stable"
-            ]
+            "maintained": false
         },
         {
             "name": "6.0",