Can't run example with Beam equal or greater than 10m

[PedroBern]

Hi, thanks for this awesome package!

If I run the example code with Beam length equal or greater than 10:

import os
from beambending import Beam, DistributedLoadV, PointLoadH, PointLoadV, x

def example_1():
    """Run example 1"""
    
    # <<< ONLY CHANGE >>>
    beam = Beam(10)  # Initialize a Beam object of length 9 m
    # <<< ONLY CHANGE >>>
    
    beam.pinned_support = 2    # x-coordinate of the pinned support
    beam.rolling_support = 7  # x-coordinate of the rolling support
    beam.add_loads((
                    PointLoadH(10, 3),  # 10 kN pointing right, at x=3 m
                    PointLoadV(-20, 3),  # 20 kN downwards, at x=3 m
                    DistributedLoadV(-10, (3, 9)),  # 10 kN/m, downwards, for 3 m <= x <= 9 m
                    DistributedLoadV(-20 + x**2, (0, 2)),  # variable load, for 0 <= x <= 2 m
                ))
    fig = beam.plot()

    # save the png and add it to the documentation
    mod_path = os.path.dirname(os.path.abspath(__file__))  # current module
    save_name = os.path.basename(__file__).replace('.py', '.png')  # file name
    save_path = os.path.join(mod_path, save_name)
    fig.savefig(save_path, transparent=True)


if __name__ == '__main__':  # call function when run as script
    example_1()

I get the following error:

Traceback (most recent call last):
  File "/Users/pedrober/.local/share/virtualenvs/pontes/lib/python3.7/site-packages/numpy/core/function_base.py", line 117, in linspace
    num = operator.index(num)
TypeError: 'float' object cannot be interpreted as an integer

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "diagrams.py", line 28, in <module>
    example_1()
  File "diagrams.py", line 18, in example_1
    fig = beam.plot()
  File "/Users/pedrober/.local/share/virtualenvs/pontes/lib/python3.7/site-packages/beambending/beam.py", line 229, in plot
    self.plot_beam_diagram(ax1)
  File "/Users/pedrober/.local/share/virtualenvs/pontes/lib/python3.7/site-packages/beambending/beam.py", line 252, in plot_beam_diagram
    self._plot_analytical(ax, sum(self._distributed_forces_y), **plot01_params)
  File "/Users/pedrober/.local/share/virtualenvs/pontes/lib/python3.7/site-packages/beambending/beam.py", line 307, in _plot_analytical
    x_vec = np.linspace(self._x0, self._x1, min(int((self.length) * 1000 + 1), 1e4))
  File "<__array_function__ internals>", line 6, in linspace
  File "/Users/pedrober/.local/share/virtualenvs/pontes/lib/python3.7/site-packages/numpy/core/function_base.py", line 121, in linspace
    .format(type(num)))
TypeError: object of type <class 'float'> cannot be safely interpreted as an integer.

If I try to plot each figure instead of plotting all together, I get the same error.