support breaking a long line

[Xingyu Lin]

In the linux shell, when the line is too long, I can use '\' to break it.

./program1 --arg1=1 \
                   --arg2=2 \
                   --arg3=3

But it seems that goreman does not support this. When I try

// Procfile 
ls: ls -a \
        -l

goreman start

I got

21:07:19 ls | Starting ls on port 5000
21:07:19 ls | ls: cannot access '\': No such file or directory
21:07:19 ls | Terminating ls