BUG: LinearRegressionwithErrors testing is not roboust enough

[bsipocz]

This maybe a sign of underlying bugs or simply just the tests are not tolerant enough. But I see this particular test function to fail occasionally.

=================================== FAILURES ===================================
_______________________ test_LinearRegressionwithErrors ________________________

    @pytest.mark.skipif('not HAS_PYMC3')
    def test_LinearRegressionwithErrors():
        """
        Test for small errors agrees with fit with y errors only
        """
    
        from astroML.linear_model import LinearRegressionwithErrors
    
        np.random.seed(0)
        X = np.random.random(10) + 1
        dy = np.random.random(10) * 0.1
        y = X * 2 + 1 + (dy - 0.05)
        dx = np.random.random(10) * 0.01
        X = X + (dx - 0.005)
    
        clf1 = LinearRegression().fit(X[:, None], y, dy)
        clf2 = LinearRegressionwithErrors().fit(np.atleast_2d(X), y, dy, dx)
    
>       assert_allclose(clf1.coef_, clf2.coef_, 0.2)
E       AssertionError: 
E       Not equal to tolerance rtol=0.2, atol=0
E       
E       Mismatched elements: 1 / 2 (50%)
E       Max absolute difference: 0.1610982
E       Max relative difference: 0.20502224
E        x: array([0.946858, 2.008877])
E        y: array([0.78576 , 2.099291])

../../astroML/linear_model/tests/test_linear_regression.py:140: AssertionError