Use the ROS 2 branch for source and doc. (#373)

Author: nuclearsandwich

crystal/distribution.yaml

@@ -149,7 +149,7 @@ repositories:
     doc:
       type: git
       url: https://github.com/BehaviorTree/BehaviorTree.CPP.git
-      version: master
+      version: ros2
     release:
       tags:
         release: release/crystal/{package}/{version}
@@ -159,7 +159,7 @@ repositories:
       test_pull_requests: true
       type: git
       url: https://github.com/BehaviorTree/BehaviorTree.CPP.git
-      version: master
+      version: ros2
     status: developed
   class_loader:
     doc: