subprojects: Update to HEAD

Change-Id: Idbc173920abc588d35be56fa7cd3171cac6673cf
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/subprojects/stdplus.wrap b/subprojects/stdplus.wrap
index 4dd1561..00dae65 100644
--- a/subprojects/stdplus.wrap
+++ b/subprojects/stdplus.wrap
@@ -1,3 +1,3 @@
 [wrap-git]
 url = https://github.com/openbmc/stdplus
-revision = master
+revision = HEAD