Fix a typo
Throw error if relation already exists
Add new lesson
Merge branch 'AdamIsrael-05-add-relations'
Merge branch 'master' into 05-add-relations
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lessons.json
Merge branch 'master' into 05-add-relations
Merge pull request #27 from AdamIsrael/05-add-relations

05 add relations