WPA concurrent write crash

[alok87]

Today with the latest master code c31dc85, WPA was seen to crash with this error once.

fatal error: concurrent map read and map write

goroutine 11672 [running]:
runtime.throw(0x16dfaec, 0x21)
        /usr/local/go/src/runtime/panic.go:1116 +0x72 fp=0xc0055f9978 sp=0xc0055f9948 pc=0x433912
runtime.mapaccess2_faststr(0x14f5de0, 0xc0003c42d0, 0xc004df5740, 0x51, 0xc00317b730, 0x413201)
        /usr/local/go/src/runtime/map_faststr.go:116 +0x47c fp=0xc0055f99e8 sp=0xc0055f9978 pc=0x412e5c
github.com/practo/k8s-worker-pod-autoscaler/pkg/queue.(*SQS).getReceiveMessageCache(...)
        /src/pkg/queue/sqs.go:277