fix(app): #45 Change path for zipfile export

[AlexAxthelm]

Change path for zipfile export. Since the code changes the working directory to output_dir, there is no need to construct a filepath without output_dir in it, since we can simply export to a simple file in the (now) working directory.

Prior to this change, zip would attempt to write to output_dir/output_dir/foo.zip, and now it writes to the path defined in the original zipfilename

Closes: #45

[AlexAxthelm]

there are implications to this on both TM and the new Webapp

To my knowledge, CTM doesn't use the zip files in any way

[cjyetman]

there are implications to this on both TM and the new Webapp

To my knowledge, CTM doesn't use the zip files in any way

True, but the code runs regardless