Bump the bootstrap epoch number.

The bpglob changes in build/blueprint submitted together with this
change make it necessary.

Test: Presubmits.
Change-Id: I3d19761ec1a199c2f77693a882f8744ce404c6de
diff --git a/ui/build/soong.go b/ui/build/soong.go
index 1c7fbac..9d5c996 100644
--- a/ui/build/soong.go
+++ b/ui/build/soong.go
@@ -49,7 +49,7 @@
 	// version of bootstrap and needs cleaning before continuing the build.  Increment this for
 	// incompatible changes, for example when moving the location of the bpglob binary that is
 	// executed during bootstrap before the primary builder has had a chance to update the path.
-	bootstrapEpoch = 0
+	bootstrapEpoch = 1
 )
 
 func writeEnvironmentFile(ctx Context, envFile string, envDeps map[string]string) error {