* in an array pattern should not be parsed as nil in ripper

After 6c0925b, it was impossible
to distinguish between the presence or absence of `*`.

    # Before the commit
    Ripper.sexp('0 in []')[1][0][2][1]  #=> [:aryptn, nil, nil, nil, nil]
    Ripper.sexp('0 in [*]')[1][0][2][1] #=> [:aryptn, nil, nil, [:var_field, nil], nil]

    # After the commit
    Ripper.sexp('0 in []')[1][0][2][1]  #=> [:aryptn, nil, nil, nil, nil]
    Ripper.sexp('0 in [*]')[1][0][2][1] #=> [:aryptn, nil, nil, nil, nil]

This commit reverts it.

parse.y

@@ -4656,7 +4656,7 @@ p_rest		: tSTAR tIDENTIFIER
                     /*%%%*/
                         $$ = 0;
                     /*% %*/
-                    /*% ripper: Qnil %*/
+                    /*% ripper: var_field(p, Qnil) %*/
                     }
                 ;
 

test/ripper/test_sexp.rb

@@ -229,7 +229,7 @@ def test_dsym
     [__LINE__, %q{ case 0; in *; end }] =>
     [:case,
       [:@int, "0", [1, 5]],
-      [:in, [:aryptn, nil, nil, nil, nil], [[:void_stmt]], nil]],
+      [:in, [:aryptn, nil, nil, [:var_field, nil], nil], [[:void_stmt]], nil]],
 
     [__LINE__, %q{ case 0; in *,a; end }] =>
     [:case,
@@ -238,7 +238,7 @@ def test_dsym
         [:aryptn,
           nil,
           nil,
-          nil,
+          [:var_field, nil],
           [[:var_field, [:@ident, "a", [1, 13]]]]],
         [[:void_stmt]],
         nil]],
@@ -426,9 +426,9 @@ def test_dsym
       [:in,
         [:fndptn,
           nil,
-          nil,
+          [:var_field, nil],
           [[:var_field, [:@ident, "a", [1, 9]]]],
-          nil],
+          [:var_field, nil]],
         nil,
         nil]],