Travis CI: Fix Travis linter errors

.travis.yml

@@ -1,3 +1,5 @@
+os: linux
+dist: bionic
 language: python
 python: 3.8
 cache: pip

DIRECTORY.md

@@ -321,6 +321,7 @@
   * [Newton Raphson](https://github.com/TheAlgorithms/Python/blob/master/maths/newton_raphson.py)
   * [Numerical Integration](https://github.com/TheAlgorithms/Python/blob/master/maths/numerical_integration.py)
   * [Perfect Square](https://github.com/TheAlgorithms/Python/blob/master/maths/perfect_square.py)
+  * [Pi Monte Carlo Estimation](https://github.com/TheAlgorithms/Python/blob/master/maths/pi_monte_carlo_estimation.py)
   * [Polynomial Evaluation](https://github.com/TheAlgorithms/Python/blob/master/maths/polynomial_evaluation.py)
   * [Prime Check](https://github.com/TheAlgorithms/Python/blob/master/maths/prime_check.py)
   * [Prime Factors](https://github.com/TheAlgorithms/Python/blob/master/maths/prime_factors.py)

maths/pi_monte_carlo_estimation.py

@@ -18,7 +18,8 @@ def random_unit_square(cls):
         """
         Generates a point randomly drawn from the unit square [0, 1) x [0, 1).
         """
-        return cls(x = random.random(), y = random.random())
+        return cls(x=random.random(), y=random.random())
+
 
 def estimate_pi(number_of_simulations: int) -> float:
     """
@@ -56,6 +57,7 @@ def estimate_pi(number_of_simulations: int) -> float:
 
     # doctest.testmod()
     from math import pi
+
     prompt = "Please enter the desired number of Monte Carlo simulations: "
     my_pi = estimate_pi(int(input(prompt).strip()))
     print(f"An estimate of PI is {my_pi} with an error of {abs(my_pi - pi)}")