fix reference links in lessons.html
fix reference links in lessons.html

rgaiacs/swc-website,swcarpentry/website,ErinBecker/website,gvwilson/website,rgaiacs/swc-website,swcarpentry/website,ErinBecker/website,ErinBecker/website,gvwilson/website,swcarpentry/website,ErinBecker/website,swcarpentry/website,rgaiacs/swc-website,rgaiacs/swc-website,rgaiacs/swc-website,swcarpentry/website,gvwilson/website,ErinBecker/website,gvwilson/website,gvwilson/website