Show combined deprecation warnings on travis (qiskit-community/qiskit-aqua#886)

* Show combined deprecation warnings on travis

* fix docstring identation

* restrict Sphinx version to < 3.0

Author: manoelmarques

qiskit/aqua/algorithms/eigen_solvers/numpy_eigen_solver.py

@@ -189,7 +189,7 @@ def _run(self):
         Returns:
             dict: Dictionary of results
         Raises:
-             AquaError: if no operator has been provided
+            AquaError: if no operator has been provided
         """
         if self._operator is None:
             raise AquaError("Operator was never provided")