Plotting the spectrum in stft model does not work. (with fix)

[matz78]

When I try to plot the result of stft, the spectrum is missing, and in
software/models_interface/stft_function.py
in lines 59 and 70 I got the error 'TypeError: slice indices must be integers or None or have an index method'
I could fix it by casting the index to int, and now the plot works again
l. 59 plt.pcolormesh(frmTime, binFreq, np.transpose(mX[:,:int(Nmaxplotfreq/fs+1)]))
l. 70 plt.pcolormesh(frmTime, binFreq, np.transpose(np.diff(pX[:,:int(Nmaxplotfreq/fs+1)],axis=1)))

[DavidAntliff]

This is a duplicate of #49

[xserra]

fixed