[Little Sisters Vocabulary] Update instructions.md (#3752)

Rephrased line 7 to omit the usage of `there's`.

Author: BethanyG

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

@@ -4,7 +4,7 @@ You are helping your younger sister with her English vocabulary homework, which
  Her class is learning to create new words by adding _prefixes_ and _suffixes_.
  Given a set of words, the teacher is looking for correctly transformed words with correct spelling by adding the prefix to the beginning or the suffix to the ending.
 
-There's four activities in the assignment, each with a set of text or words to work with.
+The assignment has four activities, each with a set of text or words to work with.
 
 
 ## 1. Add a prefix to a word