Fix assetion of an example program
Fix assetion of an example program

test-json-parser fails:
    test-json-parser.c:42: int main():
    Assertion `ts_node_child_count(array_node) == 4' failed.

`array_node` has five nodes: ([), (number), (,), (null), (]).

tree-sitter/tree-sitter,tree-sitter/tree-sitter,tree-sitter/tree-sitter,tree-sitter/tree-sitter,tree-sitter/tree-sitter,tree-sitter/tree-sitter,tree-sitter/tree-sitter