Update branches-config.json (#475)

Author: yurisasuke

branches-config.json

@@ -1,8 +1,15 @@
 {
   "versions": [
+     {
+      "branch": "release-5.10",
+      "isLatest": true,
+      "sourceFolder": "5.10-source",
+      "targetFolder": "5.10",
+      "label": "v5.10 (latest)"
+    },
     {
       "branch": "release-5.8",
-      "isLatest": true,
+      "isLatest": false,
       "sourceFolder": "5.8-source",
       "targetFolder": "5.8",
       "label": "v5.8 (latest)"