Bump relx version to 3.19.0

plugins/relx.mk

@@ -8,7 +8,7 @@
 RELX ?= $(CURDIR)/relx
 RELX_CONFIG ?= $(CURDIR)/relx.config
 
-RELX_URL ?= https://github.com/erlware/relx/releases/download/v3.5.0/relx
+RELX_URL ?= https://github.com/erlware/relx/releases/download/v3.19.0/relx
 RELX_OPTS ?=
 RELX_OUTPUT_DIR ?= _rel