fix: trailing ';' at end of input

src/Lean/Parser/Do.lean

@@ -78,7 +78,7 @@ withPosition fun pos₁ =>
     ("; "
      -- check indentation
      >> checkColGe pos₁.column "do-elements must be indented"
-     >> notFollowedByCommandToken)
+     >> notFollowedByCommandToken >> notFollowedBy eoi)
   >> optional (try ("; " >> notFollowedByTermToken >> notFollowedBy (ident <|> numLit <|> strLit <|> charLit <|> nameLit)))
 def doSeqBracketed := parser! "{" >> sepBy1 doElemParser "; " true >> "}"
 def doSeq          := doSeqBracketed <|> doSeqIndent

tests/lean/run/doTrailingAtEOI.lean

@@ -0,0 +1,6 @@
+new_frontend
+
+
+def f (x : Nat) : IO Nat := do
+IO.println x;
+pure x;