all: start v1.20.0-rc.1.devel

Change-Id: I7a88cf90c9b2ee61d6eae5019829362a7dce164f
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/221598
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/runtime/protoimpl/version.go b/runtime/protoimpl/version.go
index bb27337..8c2f4e9 100644
--- a/runtime/protoimpl/version.go
+++ b/runtime/protoimpl/version.go
@@ -53,7 +53,7 @@
 	versionMajor      = 1
 	versionMinor      = 20
 	versionPatch      = 0
-	versionPreRelease = "rc.1"
+	versionPreRelease = "rc.1.devel"
 )
 
 // VersionString formats the version string for this module in semver format.