Version bump to SD1A.210817.015.A4 [core/build_id.mk]

Change-Id: Ifaf6df3df0cb736aae97c6a6cae102ed2d80deac
diff --git a/core/build_id.mk b/core/build_id.mk
index c5ae2ef..eb41124 100644
--- a/core/build_id.mk
+++ b/core/build_id.mk
@@ -18,4 +18,4 @@
 # (like "CRB01").  It must be a single word, and is
 # capitalized by convention.
 
-BUILD_ID=SD1A.210817.015.A3
+BUILD_ID=SD1A.210817.015.A4