vi: modify voice variant Nguyen

espeak-ng-data/voices/!v/Nguyen

 language variant
 name Nguyen
 
-pitch  90 170
+pitch 95 175
 
-formant 1 87 82 76
-formant 2 94 56 42
-formant 3 93 52 130
-formant 6  40 50 50
-formant 7 60 50 60
-formant 8 100 50 40
+formant 0 100 125 100
+formant 1 96 90 80
+formant 2 97 70 90
+formant 3 97 60 90
+formant 4 97 60 90
+formant 5  75 50 90
+formant 6  90 50 100
+formant 7 100 50 100
+formant 8 100 50 100
 
-tone 900 225  1600 200 2400 150
+tone 100 200 600 150 800 100 2400 80 3600 95 5400 100