go: bump minimal version to 1.21 and handle deprecations

Go 1.18 is already EOL. go-maildir v0.5.0 requires go 1.20 at least.
Since go 1.20 is also EOL, bump the minimum required go version to the
first still supported version which is 1.21.

Go 1.20 deprecated Seed and Read in math/rand. Update the code
accordingly.

Changelog-deprecated: Support for go 1.20 and older.
Signed-off-by: Bence Ferdinandy <bence@ferdinandy.com>
Acked-by: Robin Jarry <robin@jarry.cc>

1 files changed, 0 insertions, 5 deletions

diff --git a/main.go b/main.go
index 123d360d..efdbf653 100644
--- a/main.go
+++ b/main.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"math/rand"
 	"os"
 	"runtime"
 	"sort"
@@ -303,7 +302,3 @@ loop:
 		}
 	}
 }
-
-func init() {
-	rand.Seed(time.Now().UnixNano())
-}