typechain errors when a directory in the imported path contains an integer as first character

TypeChain auto generated files are transforming paths into modules.

However, if a directory in the path starts with an Integer, this creates a module name starting with an integer, which is not valid in node and breaks TypeChain

## Examples

### importing package from node_modules

```
import {SignedAllowance} from "@0xdievardump/signed-allowances/contracts/SignedAllowance.sol";
```

```
SyntaxError: Identifier expected. (4:18)
2 | /* tslint:disable */
3 | /* eslint-disable */
> 4 | import type * as 0Xdievardump from './@0xdievardump';
| ^
```

### importing local file

```
import {$721Renderer} from "./721Renderers/$721Renderer.sol";
```

```
SyntaxError: An identifier or keyword cannot immediately follow a numeric literal. (4:21)
2 | /* tslint:disable */
3 | /* eslint-disable */
> 4 | import type * as 721Renderers from './721Renderers';
| ^
```