update knitr version in bib
update knitr version in bib

fboehm/cboettig_site,fboehm/cboettig_site,fboehm/cboettig_site,fboehm/labnotebook,fboehm/labnotebook,fboehm/labnotebook,antass/labnotebook3,fboehm/labnotebook,antass/labnotebook3,fboehm/cboettig_site,fboehm/cboettig_site,fboehm/labnotebook,fboehm/labnotebook,antass/labnotebook3