Follow-up from "Update GDK doc for enable puma by default"

The following discussion from !712 (merged) should be addressed:

• @grzesiek started a discussion: (+3 comments)

  Do we have DotEnv bundled somewhere? I couldn't find it 🤔

Tested it in GDK:

grzesiek@b953b238889d: gdk | b: master *% u= $ git diff

diff --git a/lib/run.rb b/lib/run.rb
index d3638a8..f1085c5 100644
--- a/lib/run.rb
+++ b/lib/run.rb
@@ -1,4 +1,5 @@
 def main(argv)
+  raise ENV['ABC']
   case argv[0]
   when 'db'
     foreman_exec(%w[redis postgresql openldap influxdb webpack registry minio elasticsearch jaeger])

grzesiek@b953b238889d: gdk | b: master *% u= $ ABC=xxx gdk run db
(in /home/grzesiek/gdk)
Traceback (most recent call last):
	1: from lib/run.rb:84:in `<main>'
lib/run.rb:2:in `main': xxx (RuntimeError)
grzesiek@b953b238889d: gdk | b: master *% u= $ echo 'ABC="YYY"' > .env && gdk run db
(in /home/grzesiek/gdk)
Traceback (most recent call last):
	2: from lib/run.rb:84:in `<main>'
	1: from lib/run.rb:2:in `main'
lib/run.rb:2:in `raise': exception object expected (TypeError)