fix links to lessons
fix links to lessons

Fix html links as per https://github.com/datacarpentry/datacarpentry.github.io/issues/436
ErinBecker/datacarpentry.github.io,ErinBecker/datacarpentry.github.io,ErinBecker/datacarpentry.github.io,datacarpentry/datacarpentry.github.io,ErinBecker/datacarpentry.github.io,datacarpentry/datacarpentry.github.io,datacarpentry/datacarpentry.github.io