Duplicate identifier 'out' (with clean repro)

Thanks for your work!

Here's a reproduction of the bug:

```
cd /tmp
git clone git@github.com:ShieldFinanceHQ/contracts.git
cd contracts
nvm install $(cat .nvmrc)
nvm use
npm install --global yarn
yarn install
yarn build
yarn typecheck
```

Expected output: blank (no type errors)

Actual output:

```
# Multiple errors, including:

typechain-types/UniswapV1Exchange.ts:875:59 - error TS2300: Duplicate identifier 'out'.

875 ): Promise<[BigNumber, BigNumber] & { out: BigNumber; out: BigNumber }>;
```