nano: Make revision.h a stub

* Otherwise we get an annoying git tag near nano title

Change-Id: Ie84b9ec0e1a7f1ed83051fdacf20301fc886376f
diff --git a/revision.h b/revision.h
index a68b929..b167aa0 100644
--- a/revision.h
+++ b/revision.h
@@ -1 +1 @@
-#define REVISION "v2.7.5-2-g20c86513"
+// Stub