add the root cause issue in a comment, so we know

when the workaround is no longer needed

json_rpc.nimble

@@ -20,6 +20,7 @@ proc configForTests() =
   --run
   --forceBuild
   --threads: on
+  # https://github.com/nim-lang/Nim/issues/8294#issuecomment-454556051
   if hostOS == "windows":
     --define: "chronicles_colors=NoColors"