typo/errata added

ERRATA.md

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+# Errata
+
+- Since the evaluation code for SNR contains typo 10 instead of 20, all of the paper's SNR values should be twice.
+- There is no difference that our model shows better results than other models on SNR.
+
+- page 4, Table 2
+
+Before
+
+|model|      SingleSpeaker SNR|           MultiSpeaker SNR|
+| --- | ----------- | ---------- |
+|Linear x2|9.69|11.1|
+|U-Net x2|10.3|9.86|
+|MU-GAN x2|10.5|12.3|
+|NU-Wave x2|**11.1**|**13.2**|
+|Linear x3|8.04|8.71|
+|U-Net  x3|8.81|10.7|
+|MU-GAN x3|9.44|11.7|
+|NU-Wave x3|**9.62**|**12.0**|
+
+
+After 
+|model|      SingleSpeaker SNR|           MultiSpeaker SNR|
+| --- | ----------- | ---------- |
+|Linear x2|19.38|22.2|
+|U-Net x2|20.6|19.72|
+|MU-GAN x2|21.0|24.6|
+|NU-Wave x2|**22.2**|**26.4**|
+|Linear x3|16.08|17.42|
+|U-Net  x3|17.62|21.4|
+|MU-GAN x3|18.88|23.4|
+|NU-Wave x3|**19.24**|**24.0**|
+
+- page 4, Section 5
+
+Before
+```
+Our model improves SNR value by 0.18-0.9 dB from the
+best performing baseline, MU-GAN.
+```
+
+After
+```
+Our model improves SNR value by 0.36-1.8 dB from the
+best performing baseline, MU-GAN.
+```