Minor typo fix in introduction.md

Author: gigo64

exercises/concept/little-sisters-vocab/.docs/introduction.md

@@ -166,7 +166,7 @@ Strings can also be broken into smaller strings via [`<str>.split(<separator>)`]
 >>> cat_words = "feline, four-footed, ferocious, furry"
 >>> cat_words.split(',')
 ...
-['feline', 'four-footed', 'ferocious', 'furry']
+['feline', ' four-footed', ' ferocious', ' furry']
 ```