setting cwd for inkscape subprocess uses wrong directory

[dvzrv]

While trying to do the work on #39 I tried to use the default inkscape-based compilation of the videos.
Unfortunately the subprocess call in renderlib.py sets cwd to task.workdir:

intro-outro-generator/renderlib.py

Line 97 in 789c9f5

errorReturn = subprocess.check_output(cmd, shell=True, universal_newlines=True, stderr=subprocess.STDOUT, cwd=task.workdir)

This leads to inkscape not being able to open the generated SVG files, because the path is concatenated to something like /absolute/path/to/<project_dir>/artwork/<project_dir>/artwork/.frames/.
Moreover, this does not lead to make.py (or rather renderlib.py) exiting with a non-zero exit code. The script tries to render all frames, but ultimately fails to finish any of them and is therefore also unable to render the video (the process should exit early).

For me it worked to just remove the cwd setting.