fix bug in frequency scale
fix bug in frequency scale

joshblum/eeg-spectrogram,joshblum/eeg-spectrogram,joshblum/eeg-toolkit,joshblum/eeg-toolkit,joshblum/eeg-toolkit,joshblum/eeg-toolkit,joshblum/eeg-spectrogram,joshblum/eeg-toolkit,joshblum/eeg-spectrogram,joshblum/eeg-spectrogram