Merge remote-tracking branch 'upstream/master'

Conflicts:
	source/index.html.erb
Merge branch 'master' of github.com:ruby-china/rubyconfchina.org
adjust sponsors' logo size.
limit max-width of sponsors' logos.
change favicon.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	source/index.html.erb
Adjustment position of bitfund.
Remove speaker: Vincent.