Update Makefile BUILD variable to work on systems that have different date implementation

Author: rafaelespinoza

Makefile

@@ -7,7 +7,7 @@ BASE_PATH := $(shell pwd)
 BUILD_PATH := $(BASE_PATH)/build
 BIN_DIR := $(BASE_PATH)/bin
 VERSION ?= $(shell git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\1/' | tr '/' '_')
-BUILD ?= $(shell date --utc --rfc-3339=seconds | tr ' ' 'T')
+BUILD ?= $(shell date --utc +%FT%T%z | tr ' ' 'T')
 ASSETS := static
 
 # PACKAGES