Typos in CHANGELOG.md

Merge branch 'master' of https://github.com/sendgrid/sendgrid-php

Version Bump v7.2.0: Dynamic Template Support

Version Bump v7.1.1: Fix sendgrid#667

Version Bump v7.1.0: Pre-Dynamic Template Roll Up Release

Version Bump v7.0.0: BREAKING CHANGE - please see CHANGELOG

Version Bump v6.2.0: Hacktoberfest PRs round 2

Version Bump v6.1.0: Hacktoberfest Rollup Release

Version Bump: v6.0.0: PR sendgrid#408: Update Mail constructor to sig…

…nify which parameters are required for sending all email

Version Bump v5.6.2: PR sendgrid#410: Adding name for ReplyTo for issue 

sendgrid#390