docs: Update badge link for Pub Version in README

[miquelbeltran]

docs: Update badge link for Pub Version in README

Description 📝

• Purpose: Ensures that tapping on the Pub version shield links to pub.dev
• Approach: Markdown link fixed

Type of change

• Docs update

Updates

• Updates README.md

Screenshots 📷

• None

Test plan 🧪

• Check README in preview on GH, tapping on the shield should open pub.dev

Author to check 👓

• Project and all contained modules builds successfully
• Self-/dev-tested
• Unit/UI/Automation/Integration tests provided where applicable
• Code is written to standards
• Appropriate documentation written (code comments, internal docs)

Reviewer to check ✔️

• Project and all contained modules builds successfully
• Change has been dev-/reviewer-tested, where possible
• Unit/UI/Automation/Integration tests provided where applicable
• Code is written to standards
• Appropriate documentation written (code comments, internal docs)