event-processor: make Dockerfule multiarch compatible

#7
diff --git a/events/Dockerfile b/events/Dockerfile
index fb5884c..567c77c 100644
--- a/events/Dockerfile
+++ b/events/Dockerfile
@@ -4,7 +4,6 @@
     apk add --no-cache bash git openssh
 
 ENV GOOS linux
-ENV GOARCH $BUILDPLATFORM
 ENV CGO_ENABLED 0
 ENV GO111MODULE on