Handle tables names with dashes

[macbre]

SHOW CREATE TABLE foo_bar-metadata

2018-03-12 15:16:00 indexdigest.database.query          ERROR    Database error #1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-metadata' at line 1
  File "/opt/wikia/index-digest/indexdigest/database.py", line 242, in get_table_schema
    schema = str(self.query_row('SHOW CREATE TABLE {}'.format(table_name))[1])