Include current environment variables for child processess

[narirou]

#5 (Reported by @vkareh)

[vkareh]

How is this different from #5? Do you feel the _.extend() should happen inside app.listen?

[vkareh]

The problem with adding environment variables inside a function is that it forces them to be extended during runtime, rather than during the start of the app, thus possibly preventing the app itself from overriding any environment variables it needs for its child processes. This could lead to unpredictable conditions within the node app being developed with gulp.

The _.extend() should happen outside of the scope of any function so that it represents the actual environment variables of the system.

[narirou]

I thought it is convenient to extend values inside of the function,
but you are right, environment variables might be unpredictable as you say.
I will re-open & merge your pull-request, and add more test codes.
Thanks.