nodemap: move on disk file to version 1

nodemap: move on disk file to version 1

The current format contains the information we need, lets freeze it before the
release.

Differential Revision: https://phab.mercurial-scm.org/D8416

--- a/mercurial/revlogutils/nodemap.py	Tue Apr 14 03:01:52 2020 +0200
+++ b/mercurial/revlogutils/nodemap.py	Tue Apr 14 03:05:54 2020 +0200
@@ -267,8 +267,7 @@
 # data. Its content is currently very light, but it will expand as the on disk
 # nodemap gains the necessary features to be used in production.
 
-# version 0 is experimental, no BC garantee, do no use outside of tests.
-ONDISK_VERSION = 0
+ONDISK_VERSION = 1
 S_VERSION = struct.Struct(">B")
 S_HEADER = struct.Struct(">BQQQQ")