Fix typos in the Extending Nikola doc.
Fix typos in the Extending Nikola doc.

gwax/nikola,knowsuchagency/nikola,yamila-moreno/nikola,atiro/nikola,okin/nikola,xuhdev/nikola,andredias/nikola,atiro/nikola,schettino72/nikola,lucacerone/nikola,masayuko/nikola,lucacerone/nikola,jjconti/nikola,immanetize/nikola,knowsuchagency/nikola,immanetize/nikola,andredias/nikola,gwax/nikola,xuhdev/nikola,techdragon/nikola,okin/nikola,JohnTroony/nikola,yamila-moreno/nikola,schettino72/nikola,TyberiusPrime/nikola,s2hc-johan/nikola,knowsuchagency/nikola,getnikola/nikola,lucacerone/nikola,gwax/nikola,schettino72/nikola,masayuko/nikola,x1101/nikola,techdragon/nikola,TyberiusPrime/nikola,getnikola/nikola,s2hc-johan/nikola,berezovskyi/nikola,pluser/nikola,pluser/nikola,wcmckee/nikola,atiro/nikola,techdragon/nikola,x1101/nikola,x1101/nikola,masayuko/nikola,okin/nikola,wcmckee/nikola,pluser/nikola,wcmckee/nikola,getnikola/nikola,xuhdev/nikola,berezovskyi/nikola,JohnTroony/nikola,andredias/nikola,yamila-moreno/nikola,berezovskyi/nikola,jjconti/nikola,getnikola/nikola,immanetize/nikola,TyberiusPrime/nikola,JohnTroony/nikola,s2hc-johan/nikola,okin/nikola,jjconti/nikola,xuhdev/nikola