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

@@ -5,21 +5,21 @@
     "docsSlug": "doctrine-coding-standard",
     "versions": [
         {
-            "name": "8.0",
-            "branchName": "master",
-            "slug": "latest",
-            "upcoming": true
-        },
-        {
-            "name": "7.0",
-            "branchName": "7.0.x",
-            "slug": "7.0",
+            "name": "8.1",
+            "branchName": "8.1.x",
+            "slug": "8.1",
             "current": true,
             "aliases": [
                 "current",
                 "stable"
             ]
         },
+        {
+            "name": "7.0",
+            "branchName": "7.0.x",
+            "slug": "7.0",
+            "maintained": false
+        },
         {
             "name": "6.0",
             "branchName": "6.x",