Change branch regexp

There has to be one character in the branch name

Error from LUCI:

ERROR: luci-milo.cfg: in "luci-milo.cfg" (console #2 (main_all) / regexp:refs/heads/*): fewer than 2 slashes in literal prefix "refs/heads", e.g., "refs/heads/\d+" is accepted because of "refs/heads/" is the literal prefix, while "refs/.*" is too short
Change-Id: I22d6cae6e9e6a73722d1ce7c02b9781f42561537
diff --git a/infra/config/global/luci-milo.cfg b/infra/config/global/luci-milo.cfg
index f455b72..8dc59cb 100644
--- a/infra/config/global/luci-milo.cfg
+++ b/infra/config/global/luci-milo.cfg
@@ -198,7 +198,7 @@
   id: "main_all"
   name: "R8 all"
   repo_url: "https://r8.googlesource.com/r8"
-  refs: "regexp:refs/heads/*"
+  refs: "regexp:refs/heads/.*"
   manifest_name: "REVISION"
 
   builders {