Changing the plugin does not change the ss58 address

[killbond007]

Describe the bug
Changing the plugin does not change the ss58 address , Now only support [0, 2, 7, 42]

Screenshots

Simulator.Screen.Recording.-.iPhone.12.Pro.Max.-.2021-05-08.at.09.34.33.mp4

Additional context

i think should add more ss58 in ss58List ， （Can you help add value 6 in ss58List for bifrost ）

in https://github.com/polkawallet-io/sdk/blob/6644bb7e1959987d5913eb2200a2fd9574839675/lib/storage/keyring.dart

[Shawn Yang]

fixed