feat: rewrite file modtime in zip files

pkg/zipper/zipper.go

@@ -9,6 +9,7 @@ import (
  "net/http"
  "os"
  "path/filepath"
+ "time"
 )
 
 func Zip(path string) (string, error) {
@@ -74,6 +75,11 @@ func addFileToZip(zw *zip.Writer, topPath, path string) error {
  return err
  }
 
+ // we intentionally ignore the file's modtime because if the _content_ of the zip file
+ // is the same (as determined by an md5) then we will skip an upload altogether. this
+ // date was chosen because jan 1st 1970 can sometimes look like a bug - this is deliberate.
+ fh.Modified = time.Date(1989, 4, 25, 0, 0, 0, 0, time.UTC).UTC()
+
  relPath, err := filepath.Rel(topPath, path)
  if err != nil {
  return err