Fix "No such file or directory: 'RUNS/KittiSeg_pretrained.zip'"

[hlnull]

create the "RUNS" directory to fix #19: No such file or directory: 'RUNS/KittiSeg_pretrained.zip'.

The root cause is that open() does not create a file when the file should be created in other directories. Users have to create the directories first.

[obendidi]

it's better to probably change it to :

if not os.path.exists(runs_dir):
    os.makedirs(runs_dir)

to check if the folder exists , and create it if not

[hlnull]

Thanks for advice. I just added os.path.exists().

I have not checked the train.py yet. Will do the same thing if necessary.

[hlnull]

@MarvinTeichmann
Would you please review this pr?

[MarvinTeichmann]

Looks good. Thanks!