Absolute path in eli_download_docs.sh

[tomhosking]

Bug description
Line 3 of eli_download_docs.sh changes working directory to /checkpoint/yjernite/Code/ELI5/data_creation, which only works if that's where you cloned the repo.

Reproduction steps
Clone the repo, run ./eli_download_docs_launcher.sh

Expected behavior
The path should be relative so that it works on generic clusters/machines.

Logs
Output from slurm job:

./eli_download_docs.sh: line 3: cd: /checkpoint/yjernite/Code/ELI5/data_creation: No such file or directory
python: can't open file 'download_support_docs.py': [Errno 2] No such file or directory