Add missing punctuation

specs/_features/eip7594/polynomial-commitments-sampling.md

@@ -256,7 +256,7 @@ def add_polynomialcoeff(a: PolynomialCoeff, b: PolynomialCoeff) -> PolynomialCoe
 ```python
 def neg_polynomialcoeff(a: PolynomialCoeff) -> PolynomialCoeff:
  """
- Negative of coefficient form polynomial ``a``
+ Negative of coefficient form polynomial ``a``.
  """
  return PolynomialCoeff([-x for x in a])
 ```