Fix minor typo.

app.py

@@ -51,7 +51,7 @@ type=['wav'])
             base_coqui= synth_coqui(tts_text, models[tts_lang]['coqui'])
             base_espeakng= synth_espeakng(tts_text, models[tts_lang]['espeakng'])
             base_toucan= synth_toucan(tts_text, models[tts_lang]['toucan'])
-            base_piper synth_piper(tts_text, models[tts_lang]['piper'])
+            base_piper= synth_piper(tts_text, models[tts_lang]['piper'])
 
             if tts_lang=="swh":
                 finetuned_mms1 = synth_mms(tts_text, "khof312/mms-tts-swh-female-1")