Make the builds reproducable based on commit sha

Makefile

@@ -2,8 +2,9 @@
 
 EXECUTABLE ?= drone-email
 IMAGE ?= plugins/$(EXECUTABLE)
+COMMIT ?= $(shell git rev-parse --short HEAD)
 
-LDFLAGS = -X "main.buildDate=$(shell date -u '+%Y-%m-%d %H:%M:%S %Z')"
+LDFLAGS = -X "main.buildCommit=$(COMMIT)"
 PACKAGES = $(shell go list ./... | grep -v /vendor/)
 
 all: deps build test

main.go

@@ -9,11 +9,11 @@ import (
 )
 
 var (
-	buildDate string
+	buildCommit string
 )
 
 func main() {
-	fmt.Printf("Drone Email Plugin built at %s\n", buildDate)
+	fmt.Printf("Drone Email Plugin built from %s\n", buildCommit)
 
 	system := drone.System{}
 	repo := drone.Repo{}