remove legacy ENV variables

[gdams]

removes the following warnings:

 3 warnings found (use --debug to expand):
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 22)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 23)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 48)
Dockerfile:50

refer to https://docs.docker.com/reference/dockerfile/#environment-replacement for the reference