potential data race: signals

[lmorg]

Describe the bug:

[FAILED] (unit)       10:379   signal.SIGUSR1.trap
         StderrMatch string mismatch. Got: ==================
         WARNING: DATA RACE
         Read at 0x00c0000a6378 by goroutine 21:
           github.com/lmorg/murex/builtins/events/onSignalReceived.(*sigEvents).callback()
               /Users/laurencemorgan/dev/go/src/github.com/lmorg/murex/builtins/events/onSignalReceived/onSignalReceived.go:144 +0x11c
           github.com/lmorg/murex/builtins/events/onSignalReceived.(*sigEvents).signalHandler()
               /Users/laurencemorgan/dev/go/src/github.com/lmorg/murex/builtins/events/onSignalReceived/onSignalReceived.go:203 +0x58
           github.com/lmorg/murex/builtins/events/onSignalReceived.init.0.gowrap1()
               /Users/laurencemorgan/dev/go/src/github.com/lmorg/murex/builtins/events/onSignalReceived/onSignalReceived.go:25 +0x20

         Previous write at 0x00c0000a6378 by goroutine 1256:
           github.com/lmorg/murex/builtins/events/onSignalReceived.(*sigEvents).Add()
               /Users/laurencemorgan/dev/go/src/github.com/lmorg/murex/builtins/events/onSignalReceived/onSignalReceived.go:72 +0x30c
           github.com/lmorg/murex/builtins/events.cmdEvent()
               /Users/laurencemorgan/dev/go/src/github.com/lmorg/murex/builtins/events/cmd.go:49 +0x258