Prepare the 3.8.0 release (#1438)

Author: derrabus

.doctrine-project.json

@@ -4,17 +4,23 @@
     "slug": "migrations",
     "docsSlug": "doctrine-migrations",
     "versions": [
+        {
+            "name": "3.9",
+            "branchName": "3.9.x",
+            "slug": "3.9",
+            "upcoming": true
+        },
         {
             "name": "3.8",
             "branchName": "3.8.x",
             "slug": "3.8",
-            "upcoming": true
+            "current": true
         },
         {
             "name": "3.7",
             "branchName": "3.7.x",
             "slug": "3.7",
-            "current": true
+            "maintained": false
         },
         {
             "name": "3.6",