env: fix unexpected character bug with recent docker desktop

This prevents the following parsing errors in recent Docker Desktop app:

- unexpected character "!" in variable name near "to Web Chat!\\n\\n...
- respectively: unexpected character "-" in variable name near "super-light-editor light-background full-width-editor...

Co-authored-by: Werner Fleischer <70745309+wernf@users.noreply.github.com>

env.example

@@ -101,13 +101,13 @@ TZ=UTC
 ETHERPAD_TITLE=Video Chat
 
 # The default text of a pad
-ETHERPAD_DEFAULT_PAD_TEXT=Welcome to Web Chat!\n\n
+ETHERPAD_DEFAULT_PAD_TEXT="Welcome to Web Chat!\n\n"
 
 # Name of the skin for etherpad
 ETHERPAD_SKIN_NAME=colibris
 
 # Skin variants for etherpad
-ETHERPAD_SKIN_VARIANTS=super-light-toolbar super-light-editor light-background full-width-editor
+ETHERPAD_SKIN_VARIANTS="super-light-toolbar super-light-editor light-background full-width-editor"
 
 
 #