Update module github.com/chrj/smtpd to v0.3.1

This MR contains the following updates:

Package	Type	Update	Change
github.com/chrj/smtpd	require	patch	v0.3.0 -> v0.3.1

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Release Notes

chrj/smtpd

v0.3.1

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go.mod

@@ -3,7 +3,7 @@ module git.autistici.org/ai3/tools/reports-collector
 go 1.15
 
 require (
-	github.com/chrj/smtpd v0.3.0
+	github.com/chrj/smtpd v0.3.1
 	github.com/jhillyerd/enmime v0.9.2
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/oschwald/geoip2-golang v1.5.0