Update book to current release

hamishwillee · hamishwillee · commit d06055b2b076 · 2020-05-18T16:05:32.000+10:00
diff --git a/book.json b/book.json
@@ -3,7 +3,7 @@
     "title": "MAVSDK Guide", 
     "variables": {
         "logo": "./assets/site/sdk_logo_full.png",
-        "github_branch": "develop"
+        "github_branch": "v0.25.0"
     },
     "plugins": [
         "youtube",
