Enabled using addr_make inside AppBuilder::build

[DariuszDepta]

closes #188
reported in: CosmWasm/cw-template#158

Enabled using addr_make inside AppBuilder::build, the closure passed to build function gets the same Api implementation as App, like shown below. api argument here has type cosmwasm_std::testing::mock::MockApi, exactly like the App, so using addr_make inside build is now possible.

const USER: &str = "user";
const DENOM: &str = "denom";
const AMOUNT: u128 = 100;

let app = AppBuilder::new().build(|router, api, storage| {
    router
        .bank
        .init_balance(
            storage,
            &api.addr_make(USER),
            vec![Coin {
                denom: DENOM.to_string(),
                amount: Uint128::new(AMOUNT),
             }],
         )
        .unwrap();
});

[chipshort]

Looks pretty good to me. Just two minor comments.

[chipshort]

LGTM