Specify configBridge as relative path to source
Specify configBridge as relative path to source

This adjusts the load path for the ``configBridge.json`` file from one
that's relative to the user running the command (eg ``jekyll serve``),
to one that's relative to the ``source`` configuration setting for
Jekyll.

The result is that the user can now have a (customised) ``_config.yml``
for Jekyll anywhere on her filesystem and point to Bootstrap's
``docs`` directory to use as the ``source``.  Previously, in order to
customise it, the original ``_config.yml`` needed to be modified inside
(a forked) Bootstrap, and the ``jekyll`` command could only be run at
the root of the Bootstrap package as the original file path to
``configBridge.json`` was only valid there.

The existing behaviour is not affected.

copperdesign/bootstrap,gijsbotje/bootstrap,bootstrapbrasil/bootstrap,nice-fungal/bootstrap,NCARB/bootstrap,Delagen/bootstrap,hellonewman81/bs4,sealocal/bootstrap,vitaligent/4,Hightrack/bootstrap,vsn4ik/bootstrap,davethegr8/bootstrap,copperdesign/bootstrap,lemuelbarango/bootstrap,SweetProcess/bootstrap,vsn4ik/bootstrap,realcrowd/bootstrap,Delagen/bootstrap,luistelmocosta/bootstrap,onenameio/rhythm-bootstrap,realcrowd/bootstrap,afuno/bootstrap,sealocal/bootstrap,afuno/bootstrap,andresgalante/bootstrap,supergibbs/bootstrap,coliff/bootstrap,edanbarak/bootstrap,blockstack/blockstack-bootstrap,igoynawamreh/bootstrap,TORO-IO/bootstrap,Hemphill/bootstrap-docs,GerHobbelt/bootstrap,creativewebjp/bootstrap,IdanCo/bootstrap,Delagen/bootstrap,andresgalante/bootstrap,johnajacob/bootstrap,frostbitten/bootstrap,realcrowd/bootstrap,supergibbs/bootstrap,gijsbotje/bootstrap,SweetProcess/bootstrap,Hightrack/bootstrap,nice-fungal/bootstrap,abvalentine/bootstrap,IdanCo/bootstrap,seanwu99/bootstrap,kvlsrg/bootstrap,edanbarak/bootstrap,tomlutzenberger/bootstrap,JumpLinkNetwork/bootstrap-backward,TheFridayInstitute/bootstrap,yuyokk/bootstrap,kvlsrg/bootstrap,stanwmusic/bootstrap,GerHobbelt/bootstrap,peterblazejewicz/bootstrap,xt0rted/bootstrap,luistelmocosta/bootstrap,hebbet/bootstrap,lemuelbarango/bootstrap,Lyricalz/bootstrap,luistelmocosta/bootstrap,TheFridayInstitute/bootstrap,onenameio/rhythm-bootstrap,jipexu/bootstrap,tjkohli/bootstrap,xt0rted/bootstrap,slavanga/bootstrap,lemuelbarango/bootstrap,9-chirno/chirno,vitaligent/4,frostbitten/bootstrap,hellonewman81/bs4,abvalentine/bootstrap,peterblazejewicz/bootstrap,urbit/bootstrap,gijsbotje/bootstrap,jipexu/bootstrap,Hightrack/bootstrap,abvalentine/bootstrap,xt0rted/bootstrap,vsn4ik/bootstrap,peterblazejewicz/bootstrap,zalog/bootstrap,Scoutski/bootstrap,davethegr8/bootstrap,tjkohli/bootstrap,lemuelbarango/bootstrap,andresgalante/bootstrap,edanbarak/bootstrap,mpharrigan/bootstrap,slavanga/bootstrap,tibo66/bootstrap,copperdesign/bootstrap,frostbitten/bootstrap,Scoutski/bootstrap,lipis/bootstrap,Hemphill/bootstrap-docs,zalog/bootstrap,sealocal/bootstrap,hebbet/bootstrap,joblocal/bootstrap,tomlutzenberger/bootstrap,bardiharborow/bootstrap,igoynawamreh/bootstrap,fschumann1211/bootstrap,JumpLinkNetwork/bootstrap-backward,johnajacob/bootstrap,TheFridayInstitute/bootstrap,realcrowd/bootstrap,m5o/bootstrap,coliff/bootstrap,bardiharborow/bootstrap,n054/bootstrap,creativewebjp/bootstrap,janseliger/bootstrap,wesamco/bootstrap-rtl,supergibbs/bootstrap,david-schopf/bootstrap,JumpLinkNetwork/bootstrap-backward,Scoutski/bootstrap,inway/bootstrap,wesamco/bootstrap-rtl,TheFridayInstitute/bootstrap,inway/bootstrap,joblocal/bootstrap,lipis/bootstrap,johnajacob/bootstrap,jipexu/bootstrap,slavanga/bootstrap,9-chirno/chirno,igoynawamreh/bootstrap,bardiharborow/bootstrap,twbs/bootstrap,Lyricalz/bootstrap,urbit/bootstrap,bootstrapbrasil/bootstrap,yuyokk/bootstrap,johnajacob/bootstrap,davethegr8/bootstrap,hebbet/bootstrap,tagliala/bootstrap,joblocal/bootstrap,NCARB/bootstrap,fschumann1211/bootstrap,janseliger/bootstrap,Hemphill/bootstrap-docs,janseliger/bootstrap,janseliger/bootstrap,fschumann1211/bootstrap,Lyricalz/bootstrap,nice-fungal/bootstrap,bootstrapbrasil/bootstrap,blockstack/blockstack-bootstrap,Lyricalz/bootstrap,tibo66/bootstrap,kvlsrg/bootstrap,david-schopf/bootstrap,9-chirno/chirno,stanwmusic/bootstrap,stanwmusic/bootstrap,n054/bootstrap,fschumann1211/bootstrap,seanwu99/bootstrap,inway/bootstrap,hellonewman81/bs4,tibo66/bootstrap,tagliala/bootstrap,wesamco/bootstrap-rtl,xt0rted/bootstrap,luistelmocosta/bootstrap,tagliala/bootstrap,Delagen/bootstrap,Hemphill/bootstrap-docs,creativewebjp/bootstrap,joblocal/bootstrap,TORO-IO/bootstrap,yuyokk/bootstrap,mpharrigan/bootstrap,n054/bootstrap,afuno/bootstrap,blockstack/blockstack-bootstrap,igoynawamreh/bootstrap,david-schopf/bootstrap,IdanCo/bootstrap,jipexu/bootstrap,vsn4ik/bootstrap,stanwmusic/bootstrap,zalog/bootstrap,hebbet/bootstrap,GerHobbelt/bootstrap,twbs/bootstrap,m5o/bootstrap,JumpLinkNetwork/bootstrap-backward,sealocal/bootstrap,yuyokk/bootstrap,slavanga/bootstrap,davethegr8/bootstrap,bardiharborow/bootstrap,vitaligent/4,Scoutski/bootstrap,IdanCo/bootstrap,TORO-IO/bootstrap,seanwu99/bootstrap,andresgalante/bootstrap,supergibbs/bootstrap,frostbitten/bootstrap,NCARB/bootstrap,abvalentine/bootstrap,gijsbotje/bootstrap,wesamco/bootstrap-rtl,lipis/bootstrap,SweetProcess/bootstrap,copperdesign/bootstrap,mpharrigan/bootstrap,urbit/bootstrap,seanwu99/bootstrap,edanbarak/bootstrap,lipis/bootstrap,creativewebjp/bootstrap,SweetProcess/bootstrap,n054/bootstrap,NCARB/bootstrap,tibo66/bootstrap,onenameio/rhythm-bootstrap,9-chirno/chirno,tomlutzenberger/bootstrap,afuno/bootstrap