Update Gemfile (#32147)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32147
### Summary
Got some security warnings regarding the ruby dependencies. This diff updates the packages in Gemfile.
```
GitHub has detected that a package defined in the ios/TestApp/Gemfile.lock file of the pytorch/pytorch repository contains a security vulnerability.
Package name: excon
Affected versions: < 0.71.0
Fixed in version: 0.71.0
Severity: LOW
Identifier(s):
GHSA-q58g-455p-8vw9
CVE-2019-16779
```
### Test Plan
- Won't affect the existing iOS CI jobs
Test Plan: Imported from OSS
Differential Revision: D19400087
Pulled By: xta0
fbshipit-source-id: 34b548d136cfd6b68fcc53bf0b243461bd7afd64
