Release 2.7.1

• cb6e53b - fix: check the url can be undefined Close #224
• 7275d7a - Merge pull request #227 from joolfe/issue-224
• cfcd8d8 - Merge branch 'master' of https://github.com/joolfe/postman-to-openapi into develop
• 099eb73 - fix: docs table add some spaces
• f94365f - docs: update changelog
• e0f0e35 - Merge pull request #228 from joolfe/develop