Update exercer.csl

Corrections made :
- Rights rewrited : <rights license="http://creativecommons.org/licenses/by-sa/3.0/">This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License</rights>
- Title modification: <title>exercer (French)</title>
- English and German locale sections removed
- Documentation link <link href="http://www.nlm.nih.gov/bsd/uniform_requirements.html" rel="documentation"/> removed
- ISSN ascended