fix: do not ban .. with a . on the next line

Without this change,
```lean
example : True := by
  refine' trivial ..
  . trivial
```
is a parse error.

src/Lean/Parser/Term.lean

@@ -752,7 +752,7 @@ We use them to implement `macro_rules` and `elab_rules`
 def namedArgument  := leading_parser (withAnonymousAntiquot := false)
   atomic ("(" >> ident >> " := ") >> withoutPosition termParser >> ")"
 def ellipsis       := leading_parser (withAnonymousAntiquot := false)
-  ".." >> notFollowedBy "." "`.` immediately after `..`"
+  ".." >> notFollowedBy (checkNoWsBefore >> ".") "`.` immediately after `..`"
 def argument       :=
   checkWsBefore "expected space" >>
   checkColGt "expected to be indented" >>