Update branch metadata

3.1.0 has been released. As a result,

- 3.2.x is the next minor branch;
- 3.1.x is the current branch;
- 3.0.x is no longer maintained.

Author: greg0ire

.doctrine-project.json

@@ -10,17 +10,22 @@
       "slug": "latest",
       "upcoming": true
     },
+    {
+      "name": "3.2",
+      "branchName": "3.2.x",
+      "slug": "3.2",
+      "upcoming": true
+    },
     {
       "name": "3.1",
       "branchName": "3.1.x",
       "slug": "3.1",
-      "upcoming": true
+      "current": true
     },
     {
       "name": "3.0",
-      "branchName": "3.0.x",
       "slug": "3.0",
-      "current": true
+      "maintained": false
     },
     {
       "name": "2.19",