Cleaning-up Vietnamese translation (#1086)

* Cleaning-up the translation

* Update app_piano.lua

* Update lang_vi.lua

* Update TVN's link

I feel bruh because I should at least realize that TVN server lost it's Tier-3 boost a long time ago

* Small changes in dict.lua

* Small update in dict_vi.lua

* Remove a redundant "do-end"

parts/scenes/app_piano.lua

@@ -98,6 +98,7 @@ function scene.enter()
 end
 
 function scene.leave()
+    showingKey=false
     TABLE.clear(textObj)
     TABLE.clear(pianoVK)
     collectgarbage()
@@ -217,8 +218,7 @@ generateVKey=function()
 
                 if activateState~=nil then self.activateState=activateState
                 elseif (self.activateState==1 and activationTime==maxTime) or not self.activateState then self.activateState=0 end
-                -- LIKELY NOT POSSIBLE TO DO
-                -- Holding key: self.activateState=activateState and activateState or not activationTime>maxTime and self.activateState or 0 end
+                -- TODO: when the note can be extended longer, this will need remaking
                 if dt then
                     if self.activateState>0 then self.ATV=min(activationTime+dt*60,maxTime)
                     elseif activationTime>0 then self.ATV=max(activationTime-dt*30,0)
@@ -238,4 +238,4 @@ generateVKey=function()
     pianoVK.shift:setObject(CHAR.key.shift)
 end
 
-return scene
+return scene