Cryptopia create_limit_buy_order failing with an exception

When using the Python version of the library, create_limit_buy_order() fails with the following exception:

Traceback (most recent call last):
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.3.2\helpers\pydev\_pydevd_bundle\pydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<input>", line 1, in <module>
  File "D:\Development\crypto-p1\venv\lib\site-packages\ccxt\base\exchange.py", line 1009, in create_limit_buy_order
    return self.create_order(symbol, 'limit', 'buy', *args)
  File "D:\Development\crypto-p1\venv\lib\site-packages\ccxt\cryptopia.py", line 354, in create_order
    'Amount': self.amount_to_precision(symbol, amount),
  File "D:\Development\crypto-p1\venv\lib\site-packages\ccxt\base\exchange.py", line 780, in amount_to_precision
    return self.truncate(amount, self.markets[symbol]['precision']['amount'])
  File "D:\Development\crypto-p1\venv\lib\site-packages\ccxt\base\exchange.py", line 436, in truncate
    return '{0:f}'.format(Decimal(num).quantize(math.pow(10, -precision)))
TypeError: conversion from float to Decimal is not supported

The issue is that the precision argument in Decimal.quantize(precision) should be of Decimal type rather than a float.

I’m not sure if this issue affects other exchanges, seeing that it is present in exchange.py.

[maltium]

I confirm that it works.

Thank you for the prompt fix.

[maltium]

Please note that commit 4aa1980 does not fix this issue. The cryptopia exchange uses the truncate(num, precision=0) method rather than truncate_to_string(num, precision=0).