math/py-sympy: Update to 1.3

Backwards compatibility breaks and deprecations:

    * Symbols no longer automatically convert to functions when called,
      e.g., if f = Symbol('f'), f(t) is now a TypeError. To create a
      function, use f = Function('f') or f = symbols('f', cls=Function).

    * .integrate() has been renamed to .compute_expectation() in
      sympy.stats in order to avoid confusion with the integrals module.

    * classof() and a2idx() in sympy.matrices.matrices have been
      deprecated in favor of the same functions in sympy.matrices.common.

    * The source() function has been deprecated. Use inspect.getsource or
      ?? in IPython.

See the release notes for the full list of changes.

    https://github.com/sympy/sympy/wiki/release-notes-for-1.3

(minskim)