fix numeric need be float

[Lu-Yi-Hsun]

in this sample deriv can input float amount like 2.5 but the code numeric is change to int() 2, so change numeric to float can fix

proposal = await api.proposal({"proposal": 1, "amount": 100, "barrier": "+0.1", "basis": "payout",
                                   "contract_type": "CALL", "currency": "USD", "duration": 60, "duration_unit": "s",
                                   "symbol": "R_100"})
print(proposal) 

[PeterOwira]

This is sufficient it worked on my end