Prepare release 3.7.0 (#6165)

Author: derrabus

.doctrine-project.json

@@ -11,17 +11,23 @@
             "slug": "latest",
             "upcoming": true
         },
+        {
+            "name": "3.8",
+            "branchName": "3.8.x",
+            "slug": "3.8",
+            "upcoming": true
+        },
         {
             "name": "3.7",
             "branchName": "3.7.x",
             "slug": "3.7",
-            "upcoming": true
+            "current": true
         },
         {
             "name": "3.6",
             "branchName": "3.6.x",
             "slug": "3.6",
-            "current": true
+            "maintained": false
         },
         {
             "name": "3.5",