Remove LegacyKeyValueFormat warnings once and for all

[psilabs-dev]

example of warnings

 4 warnings found (use docker --debug to expand):
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 6)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 9)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 12)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 13)

[Difegue]

Completely forgot about those! Thanks. I doubt docker will every be able to get rid of the old syntax though :^)