Update Mathlib/Combinatorics/Enumerative/Pentagonal.lean

Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>

Author: wwylele

Mathlib/Combinatorics/Enumerative/Pentagonal.lean

@@ -23,7 +23,7 @@ convention, but implicitly shows the monotonicity in `pentagonal_lt_pentagonal_n
 
 ## TODO
 
-Show the relation between pentagonal numbers and partitions, including pentagonal number theorem.
+Show the relation between pentagonal numbers and partitions, including the pentagonal number theorem.
 
 ## References