Update default ja vocoder

Author: erogol

TTS/.models.json

@@ -157,7 +157,7 @@
             "kokoro": {
                 "tacotron2-DDC": {
                     "github_rls_url": "https://github.com/coqui-ai/TTS/releases/download/v0.0.15/tts_models--jp--kokoro--tacotron2-DDC.zip",
-                    "default_vocoder": "vocoder_models/universal/libri-tts/wavegrad",
+                    "default_vocoder": "vocoder_models/ja/kokoro/hifigan_v1",
                     "description": "Tacotron2 with Double Decoder Consistency trained with Kokoro Speech Dataset.",
                     "author": "@kaiidams",
                     "commit": "401fbd89"