Updating PySlurm for New Slurm Releases

cd /path/to/slurm
git pull
git diff slurm-17-02-0-1 slurm-17-02-3-1 -- slurm/slurm.h.in
git diff slurm-17-02-0-1 slurm-17-02-3-1 -- src/api/*.c
git diff slurm-17-02-0-1 slurm-17-02-3-1 -- src/common/slurm_protocol_defs.c

• increment max_slurm_hex_version in setup.py
• add new version .travis.yml
• increment pyslurm/__version__.py
• update README.rst with latest supported version