ADXIndicator.adx_pos / adx_neg head assertion failed

[mike1936]

Problem

The first non-zero +DI14 is missing when try to calculating them using ADXIndicator.adx_pos.
Same problem with -DI14 and ADXIndicator.adx_neg.

Expectation:

After inserting the following test function to TestADXIndicator in ./test/unit/trend.py, the test should pass

# ...

    def test_adx_pos3(self):
        target = "+DI14"
        result = adx_pos(**self._params)
        pd.testing.assert_series_equal(
            self._df[target].head(15), result.head(15), check_names=False
        )

    def test_adx_neg3(self):
        target = "-DI14"
        result = self._indicator.adx_neg()
        pd.testing.assert_series_equal(
            self._df[target].head(16), result.head(16), check_names=False
        )

# ...