reduced number of test failure cases for hyperu
Merge pull request #2934 from gertingold/gh-2287

ENH: special: reduce number of test failure cases for hyperu

As was mentioned in gh-2909, there exists still a pretty large number of test cases for hyperu which fail. One of the reasons is the evaluation of the integral representation of U by means of Gauss-Legrendre quadrature which is done for A>=0. However, for 1>A>=0, the integrand has an integrable divergence at zero which prevents the Gauss-Legendre quadrature from converging. This PR adjusts the condition on A accordingly.