Update science.csl

Change journal article suffix to ". " from ", " following the Science citation style: 

Titles of cited articles can now be included, with words in lower case except for proper nouns, followed by a period. 

http://www.sciencemag.org/site/feature/contribinfo/prep/res/refs.xhtml
Merge pull request #992 from mccauleylab/patch-1

Update science.csl