Use static default timezone for new 'fabric' project

instead of making that part of the generated code

rattail/projects/fabric/machines/theo-server/fabenv.py.dist.mako

@@ -20,7 +20,9 @@ env.machine_is_live = False
 # stable
 <%text>##############################</%text>
 
-env.timezone = '${timezone}'
+# for a list of possible time zone values, see
+# https://en.wikipedia.org/wiki/List_of_tz_database_time_zones#List
+env.timezone = 'America/Chicago'
 
 # default sender and recipients for all emails
 env.email_default_sender = 'rattail@localhost'