Three small typos

line 10 :  to this lesson contains and 'almost' finished version of it. ---->  'and' should be 'an'

line 32 : generate sinlge numerical values -->  'sinlge' should be 'single'

line 32 : you will be able to select on of them --> 'on' should be 'one'
Merge pull request #416 from DiGro/patch-6

Three small typos