Update betterproto and generated code

Author: abn

poetry.lock

@@ -33,7 +33,7 @@ black = "^19.10b0"
 pre-commit = { version = "^2.3.0", python = "^3.6.1" }
 pytest = "^5.4"
 pytest-asyncio = "^0.12"
-betterproto = { version = "^2.0.0b1", allow-prereleases = true, extras = ["compiler"] }
+betterproto = { version = "^2.0.0b2", allow-prereleases = true, extras = ["compiler"] }
 
 [tool.black]
 line-length = 88