fix build date format for version command (#745)

Signed-off-by: cpanato <ctadeu@gmail.com>

Makefile

@@ -30,7 +30,7 @@ RUNTIME_IMAGE ?= gcr.io/distroless/static
 GIT_VERSION ?= $(shell git describe --tags --always --dirty)
 GIT_HASH ?= $(shell git rev-parse HEAD)
 GIT_TAG ?= dirty-tag
-DATE_FMT = +'%Y-%m-%dT%H:%M:%SZ'
+DATE_FMT = +%Y-%m-%dT%H:%M:%SZ
 SOURCE_DATE_EPOCH ?= $(shell git log -1 --pretty=%ct)
 ifdef SOURCE_DATE_EPOCH
     BUILD_DATE ?= $(shell date -u -d "@$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)" 2>/dev/null || date -u -r "$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)" 2>/dev/null || date -u "$(DATE_FMT)")