Updates to tap-mssql

[divv]

Changes

• Bump version of pymssql to 2.2.1 …
• Do not set the maxLength property of a string if the character_maximum_length is -1 (indicating a "max" field)
• Move 'real' from BYTES_FOR_INTEGER_TYPE to FLOAT_TYPES
• Increase maximum scale of Number data types to 17 to allow for doubles
• Move 'money' to DECIMAL_TYPES
• Get primary_keys from common.get_key_properties()