chore(Dockerfile): Download envtpl from github

Author: Jonathan Chauncey

telegraf/rootfs/Dockerfile

@@ -8,8 +8,8 @@ RUN apk --update add bash
 # The download links for the zip of telegraf are broken.
 # So for now Im building this locally and copying it into the build context.
 ADD https://bintray.com/artifact/download/jchauncey/telegraf/telegraf/telegraf /telegraf
+ADD https://github.com/arschles/envtpl/releases/download/0.1.1/envtpl_linux_amd64 /envtpl
 COPY start-telegraf /start-telegraf
-COPY envtpl /envtpl
 COPY config.toml.tpl /config.toml.tpl
 
 RUN chmod +x /telegraf