Fix misspelled backer (Nikola Trifunovic) (#3081)

My name is Nikola not "Nokola" :) Keep up the good work ;)

backers.md

@@ -114,7 +114,7 @@ It could be you!
 - Guido H.
 - Joan Cejudo
 - Ian Walter
-- Nokola Trifunovic
+- Nikola Trifunovic
 - Nicolas Mutis Mesa
 - Fahed Toumi
 - James