change default prune retention to 30 versions

you can actually remove them all from s3 and it does nothing, Lambda copies
them internally to its own storage

Author: tj

docs/06-commands.md

@@ -825,18 +825,18 @@ Flags:
       --format="text"    Output formatter.
       --version          Show application version.
   -s, --stage="staging"  Target stage name.
-  -r, --retain=60        Number of versions to retain.
+  -r, --retain=30        Number of versions to retain.
 ```
 
 ### Examples
 
-Prune and retain the most recent 15 staging versions.
+Prune and retain the most recent 30 staging versions.
 
 ```
 $ up prune
 ```
 
-Prune and retain the most recent 60 production versions.
+Prune and retain the most recent 30 production versions.
 
 ```
 $ up prune -s production

internal/cli/prune/prune.go

@@ -11,12 +11,12 @@ import (
 func init() {
 	cmd := root.Command("prune", "Prune old S3 deployments of a stage.")
 
-	cmd.Example(`up prune`, "Prune and retain the most recent 15 staging versions.")
-	cmd.Example(`up prune -s production`, "Prune and retain the most recent 60 production versions.")
+	cmd.Example(`up prune`, "Prune and retain the most recent 30 staging versions.")
+	cmd.Example(`up prune -s production`, "Prune and retain the most recent 30 production versions.")
 	cmd.Example(`up prune -s production -r 15`, "Prune and retain the most recent 15 production versions.")
 
 	stage := cmd.Flag("stage", "Target stage name.").Short('s').Default("staging").String()
-	versions := cmd.Flag("retain", "Number of versions to retain.").Short('r').Default("60").Int()
+	versions := cmd.Flag("retain", "Number of versions to retain.").Short('r').Default("30").Int()
 
 	cmd.Action(func(_ *kingpin.ParseContext) error {
 		c, p, err := root.Init()