regular expression matching in filter field seems to have problem about cloud-build-notifiers

[LOZORD]

I think the match part of your filter is incorrect -- I think you need to double-escape the back slashes like \\d. I was able to get it get a successful match test case with the following (I'll make a PR for the case shortly).

filter:    `build.status in [Build.Status.FAILURE, Build.Status.TIMEOUT] && build.substitutions["TAG_NAME"].matches("^v\\d{1}\\.\\d{1}\\.\\d{3}$")`
build:     &cbpb.Build{Status: cbpb.Build_TIMEOUT, Substitutions: map[string]string{"TAG_NAME": "v1.2.003"}},

[ggprod]

Thanks again @LOZORD ! Double backslashes solved the problem and it works as expected now.