Incorrectly handling error path in the pipeline when handling arrays.

[starrify]

Version being used: 2a1d434
Sample code to test with:

# coding: utf8

from scrapy_jsonschema import JsonSchemaItem, JsonSchemaValidatePipeline


class TestItem(JsonSchemaItem):
    jsonschema = {
        "$schema": "http://json-schema.org/draft-04/schema",
        "type": "object",
        "properties": {
            "test": {
                "type": "array",
                "items": {
                    "type": "string",
                },
            },
        },
    }


def test():
    item = TestItem()
    item['test'] = [1]
    stats = type('', (), {})
    stats.inc_value = lambda x: x
    pipeline = JsonSchemaValidatePipeline(stats)
    pipeline.process_item(item, None)


if __name__ == '__main__':
    test()

Expected result: An exception DropItem raised with message "schema validation failed: xxx".
Actual result:

Traceback (most recent call last):
  File "test.py", line 32, in <module>
    test()
  File "test.py", line 27, in test
    pipeline.process_item(item, None)
  File "/home/pengyu/temp/virtualenv/lib/python2.7/site-packages/scrapy_jsonschema/pipeline.py", line 33, in process_item
    path = '.'.join(absolute_path)
TypeError: sequence item 1: expected string, int found

[VMRuiz]

This issue is fixed in the last commit