lib/flagutil: avoid int overflow for arch 386 (#710)

Arch 386 is a 32-bit architecture and interprets int type for numbers as an explicit int32,
whereas on most modern CPUs int is implicitly an int64. This makes tests to fail with
`int overflow` error.

lib/flagutil/bytes_test.go

@@ -46,9 +46,9 @@ func TestBytesSetSuccess(t *testing.T) {
 	f("1KiB", 1024)
 	f("1.5kib", 1.5*1024)
 	f("23MiB", 23*1024*1024)
-	f("5.25GiB", 5.25*1024*1024*1024)
+	f("0.25GiB", 0.25*1024*1024*1024)
 	f("1KB", 1000)
 	f("1.5kb", 1.5*1000)
 	f("23MB", 23*1000*1000)
-	f("5.25GB", 5.25*1000*1000*1000)
+	f("0.25GB", 0.25*1000*1000*1000)
 }