Fix TextField Sortable/Nostem bug

[cheeseandcereal]

Fixes #31

Tests included

Before:

Traceback (most recent call last):
  File "test.py", line 5, in <module>
    r.create_index([field])
  File "/usr/local/lib/python3.7/dist-packages/redisearch/client.py", line 198, in create_index
    return self.redis.execute_command(*args)
  File "/usr/local/lib/python3.7/dist-packages/redis/client.py", line 839, in execute_command
    return self.parse_response(conn, command_name, **options)
  File "/usr/local/lib/python3.7/dist-packages/redis/client.py", line 853, in parse_response
    response = connection.read_response()
  File "/usr/local/lib/python3.7/dist-packages/redis/connection.py", line 718, in read_response
    raise response
redis.exceptions.ResponseError: Could not parse field spec

After:

{'index_name': 'test', 'index_options': [], 'fields': [[b'test', b'type', b'TEXT', b'WEIGHT', b'1', b'SORTABLE', b'NOSTEM']], 'num_docs': '0', 'max_doc_id': '0', 'num_terms': '0', 'num_records': '0', 'inverted_sz_mb': '0', 'offset_vectors_sz_mb': '0', 'doc_table_size_mb': '0', 'sortable_values_size_mb': '0', 'key_table_size_mb': '1.239776611328125e-05', 'records_per_doc_avg': '-nan', 'bytes_per_record_avg': '-nan', 'offsets_per_term_avg': '-nan', 'offset_bits_per_record_avg': '-nan', 'gc_stats': [b'current_hz', b'10', b'bytes_collected', b'0', b'effectiv_cycles_rate', b'0'], 'cursor_stats': [b'global_idle', 0, b'global_total', 0, b'index_capacity', 128, b'index_total', 0]}

test.py used above for reference:

import redisearch

r = redisearch.Client("test")
field = redisearch.TextField("test", sortable=True, no_stem=True)
r.create_index([field])
print(r.info())