Version Bump v5.1.0: sendgrid#173: Update ruby-http-client dependency

Version Bump v5.0.0: BREAKING CHANGE - see CHANGELOG

Version Bump: 4.3.3: sendgrid#157: Specify required ruby version as '…

…>= 2.2'

Version Bump v4.3.2: sendgrid#161: Fixed problematic Sinatra dependency

Version Bump v4.3.1: sendgrid#160: Updated sinatra version to 2.0

Merge pull request sendgrid#70 from kernkw/settings_helper

Adds an account settings management helper object

Version Bump v4.2.1: sendgrid#112: Fixes version ambiguity in gemspec

Version v4.2.0: sendgrid#148, sendgrid#146 Set api_key to empty string

Version Bump v4.1.1: sendgrid#115 sendgrid#134: Fix typos in initiali…

…ze methods

Fix date in CHANGELOG