Update README.md - fix typos in AWS Cost Explorer community server

[aarora79]

Description

fix typos in AWS Cost Explorer community server

Server Details

• Server: None
• Changes to: README.md

Motivation and Context

Fix typo.

How Has This Been Tested?

Yes

Breaking Changes

None

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• [xI have updated the server's README accordingly
• have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

None