extraneous .replace in encodeRequestToS3Key

for https://github.com/dwelch2344/cve-ref-archival/blob/24ca51169ff07766fc5d35a2ab3bc8b2a47c195c/src/engine/aws/s3.ts#L50
```
const safePath = pathname.replace(/[^\w\-\.]/g, '-').replace(/\/+/g, '_');
```
A / character is converted to a - character by the first .replace call, so the second .replace will never replace / with _