Added space to comma for str.split()

Author: BethanyG

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

@@ -164,9 +164,9 @@ Strings can also be broken into smaller strings via [`<str>.split(<separator>)`]
 
 
 >>> cat_words = "feline, four-footed, ferocious, furry"
->>> cat_words.split(',')
+>>> cat_words.split(', ')
 ...
-['feline', ' four-footed', ' ferocious', ' furry']
+['feline', 'four-footed', 'ferocious', 'furry']
 ```