Slack Notfication is not working.

Hi,
Using the latest Burrow, Configured for slack but its not working. please let me know where its failing

#[notifier.slack]
#class-name="slack"
#interval=30
#threshold=3
#timeout=5
#keepalive=30
#channel="******"
#username="**********"
#template-open="/app/burrow/config/default-slack-post.tmpl"
#url-open="******"

```
[go@negocd-wc-4p burrow]$ cat burrow.out.2018-03-30_19:18:59
panic: Unknown notifier className provided: slack [recovered]
panic: Unknown notifier className provided: slack [recovered]
panic: Unknown notifier className provided: slack

goroutine 1 [running]:
main.handleExit()
/home/travis/gopath/src/github.com/linkedin/Burrow/main.go:63 +0x293
panic(0x8f8c00, 0xc42022c220)
/home/travis/.gimme/versions/go1.9.2.linux.amd64/src/runtime/panic.go:491 +0x283
github.com/linkedin/Burrow/vendor/go.uber.org/zap/zapcore.(*CheckedEntry).Write(0xc420098370, 0x0, 0x0, 0x0)
/home/travis/gopath/src/github.com/linkedin/Burrow/vendor/go.uber.org/zap/zapcore/entry.go:229 +0x52e
github.com/linkedin/Burrow/vendor/go.uber.org/zap.(*Logger).Panic(0xc42005afc0, 0xc420012ff0, 0x2a, 0x0, 0x0, 0x0)
/home/travis/gopath/src/github.com/linkedin/Burrow/vendor/go.uber.org/zap/logger.go:225 +0x7f
github.com/linkedin/Burrow/core.configureCoordinators.func1(0xc42005a9c0)
/home/travis/gopath/src/github.com/linkedin/Burrow/core/burrow.go:96 +0x87
panic(0x8f8c00, 0xc42022c210)
/home/travis/.gimme/versions/go1.9.2.linux.amd64/src/runtime/panic.go:491 +0x283
github.com/linkedin/Burrow/core/internal/notifier.getModuleForClass(0xc42005a9c0, 0xc42014be78, 0x5, 0xc42014b130, 0x5, 0x0, 0x0, 0xc42022e300, 0xc420059340, 0x0, ...)
/home/travis/gopath/src/github.com/linkedin/Burrow/core/internal/notifier/coordinator.go:147 +0xa6b
github.com/linkedin/Burrow/core/internal/notifier.(*Coordinator).Configure(0xc4200ec600)
/home/travis/gopath/src/github.com/linkedin/Burrow/core/internal/notifier/coordinator.go:230 +0x714
github.com/linkedin/Burrow/core.configureCoordinators(0xc42005a9c0, 0xca49a0, 0xc420058e80, 0xca4960, 0xc42015c930, 0xca4760, 0xc4200d57e0, 0xca4820, 0xc4200d5840, 0xca4860, ...)
/home/travis/gopath/src/github.com/linkedin/Burrow/core/burrow.go:103 +0x9c
github.com/linkedin/Burrow/core.Start(0xc42005a9c0, 0xc42005a900, 0x0)
/home/travis/gopath/src/github.com/linkedin/Burrow/core/burrow.go:148 +0x372
main.main()
/home/travis/gopath/src/github.com/linkedin/Burrow/main.go:107 +0x401
```

Start with core/internal/notifier/coordinator.go, especially getModuleForClass and Coordinator.Configure, then trace how core/burrow.go configures coordinators. Reproduce the panic with the provided Slack configuration and determine what allows the notifier to initialize without the Unknown notifier className error.

Written by the indexing model from the issue text.