x/group: typo in flag help stirng

[hallazzang]

According to --exec flag's help string it suggests to specify 1 to try executing the proposal immediately, but this is not true.

cosmos-sdk/x/group/client/cli/tx.go

Line 537 in 3a03804

cmd.Flags().String(FlagExec, "", "Set to 1 to try to execute proposal immediately after creation (proposers signatures are considered as Yes votes)")

When I passed --exec 1 nothing happened.

And I realized that I needed to pass try instead.

cosmos-sdk/x/group/client/cli/util.go

Lines 56 to 63 in 3a03804

	func execFromString(execStr string) group.Exec {
	exec := group.Exec_EXEC_UNSPECIFIED
	if execStr == ExecTry {
	exec = group.Exec_EXEC_TRY
	}
	return exec
	}

So we need to change the help string to:

`Set to "try" to try to execute proposal immediately after creation (proposers signatures are considered as Yes votes)`