Enforce a CI test with scipy<1.5
Enforce a CI test with scipy<1.5

There are "breaking" changes within the scipy private code which various
parts of QuTiP depended on (see gh-1298, gh-1301 and commits 46e04a1,
6c85261 and 663d7d2).  We ensure that at least one test on Travis uses a
scipy version before 1.5 so that we always maintain support for it - the
other tests will typically install scipy>=1.5.

This particular test is chosen by elimination

- we want the "default" case testing against the newest versions of
  Python to use the newest versions of the libraries available,

- we want the Cython parts to be tested against both versions of scipy,
  since we link against their versions of LAPACK/BLAS.

- the Mac tests (at the time of writing) skip some tests which are
  problematic because of intermittent segfaults, including at least one
  which has issues with scipy 1.5.  The MKL/OMP one skips some tests,
  but not any which use scipy.

cgranade/qutip,cgranade/qutip,qutip/qutip,qutip/qutip