Increase MaxValidators to 108

This proposal is about increasing the Maximum Number of Validators on IRIS Hub. Once this proposal passes, the number of active validators on the IRIS Hub mainnet will be increased from 100 to 108, which gives more validators the opportunity to participate in contributing to the network security, further boosting the constant expansion of IRISnet ecosystem. In the Cosmos ecosystem, IRIS Hub is virtually one of the few mainnets where the active validator always reaches the maximum number. Currently, there are 100 active validators on IRIS Hub mainnet. And this proposal intends to increase the maximum number so that there will be more validators allowed to join IRISnet ecosystem and then better support the network decentralization.