Fix test function Rosenbrock

[beastraban]

Experiment running with Rosenbrock function yields the following error message:

`Run experiment for 'RandomOptimisation' on function 'Rosenbrock'...
/home/dm/DarkMachines/high-dimensional-sampling/examples/random_optimisation.py:50: RuntimeWarning: invalid value encountered in add
x = x * (r[:, 1] - r[:, 0]) + r[:, 0]
/home/dm/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/functions.py:186: RuntimeWarning: invalid value encountered in less
if np.any(d < 0.0) or np.any(d > 1.0):
/home/dm/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/functions.py:186: RuntimeWarning: invalid value encountered in greater
if np.any(d < 0.0) or np.any(d > 1.0):
Traceback (most recent call last):

File ~/DarkMachines/high-dimensional-sampling/examples/random_optimisation.py:75 in
experiment.run(function, finish_line=1000)

File ~/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/experiments.py:247 in run
self._perform_experiment(function, log_data)

File ~/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/experiments.py:114 in _perform_experiment
self._event_new_samples(x, y)

File ~/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/experiments.py:352 in _event_new_samples
self.best_x, self.best_y = self._find_minima(x, y, self.best_x,

File ~/anaconda3/envs/DarkMachine/lib/python3.8/site-packages/high_dimensional_sampling/experiments.py:317 in _find_minima
return x_candi[indices], y_candi[indices]

IndexError: arrays used as indices must be of integer (or boolean) type
`

For some reason I cannot debug anything in this project, :(

[beastraban]

The problem seems to be in the ranges of the Rosenbrock function being defined as -inf,inf,
whereas the sampling procedure undergoes the following transformation:
'x=x*(r[:,1]-r[:,0])+r[:,0]'
in get_initial_position (line 50) in random_optimization.py