all: start v1.27.0-devel

Change-Id: I7f2f94ed40c71582838fe6ffcb103b9e98a49d1c
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/330871
Trust: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Damien Neil <dneil@google.com>

internal/version/version.go

@@ -54,7 +54,7 @@ const (
 	Major      = 1
 	Minor      = 27
 	Patch      = 0
-	PreRelease = ""
+	PreRelease = "devel"
 )
 
 // String formats the version string for this module in semver format.