Got an exception when CATEGORICAL outcomes length are more than 6.

I am trying to create a market as follows.
```
{
"title": "test-part2。",
"description": "test",
"resolutionDate": "2019-09-29T00:00:00.000Z",
"outcomeType": "CATEGORICAL",
"outcomes": [
"outcome 1",
"outcome 2",
"outcome 3",
"outcome 4",
"outcome 5",
"outcome 6"
],
"currency": "WETH",
"fee": "0",
"funding": "1e18"
}
```
Got an exception.
```
[Gnosis SDK] EventFactory(0x0f60..f086).createCategoricalEvent("0xd19bce9f7693598a9fa1f94c548b20887a33f141", "0x95283e33901fcdc06baa21fc8156d2c8744a01df", 6, {"title":"test-part2。","description":"test","resolutionDate":"2019-09-29T00:00:00.000Z","outcomeType":"CATEGORICAL","outcomes":["outcome 1","outcome 2","outcome 3","outcome 4","outcome 5","outcome 6"],"currency":"WETH","fee":"0","funding":"1e18","costs":[{"method":"createOracle","cost":350373}],"ipfsHash":"Qmb2PWjqR3KkY45WVvbVRFnnmDzcZY4jV2sTxatS1fFMSC","oracleAddress":"0x95283e33901fcdc06baa21fc8156d2c8744a01df","gasPrice":"1000000000"})

with transaction hash 0x498b9d7450c4e45a4db00b05e07afb8f494e0e71c69beef3e30e5b683ea21a00

failed with Error: could not find any logs in transaction 0x498b9d7450c4e45a4db00b05e07afb8f494e0e71c69beef3e30e5b683ea21a00 corresponding to event CategoricalEventCreation
```
And I have checked the requirement at EventFactory.sol. It should be passed.
https://github.com/gnosis/pm-contracts/blob/v1/contracts/Events/EventFactory.sol#L55

Thanks.