icwt can't produce the same waveform

```
import pycwt as wavelet
dt=0.002
mother = wavelet.DOG()
coefs, scales, freqs, coi, fft, fftfreqs = wavelet.cwt(wave, dt,
                                                      mother,freqs=np.arange(2,10,0.2))
iwave = wavelet.icwt(coefs, scales, dt, scales[0]-scales[1], mother)
```
The waveform changed a lot