Update dependency supertest to v6.3.3

This MR contains the following updates:

Package	Type	Update	Change
supertest	devDependencies	minor	6.2.4 -> 6.3.3

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Release Notes

visionmedia/supertest (supertest)

v6.3.3

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• chore: bump deps 2910f73

v6.3.2

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• docs: added maintainer note e24875d
• docs: fixed links 5b59ddc

v6.3.1

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• fix: bump superagent (closes #​798) 25122e6

v6.3.0

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• fix: lint package.json, added files array 20adbc1
• Merge pull request #​793 from lamweili/feat/http2 22b89b6
• Merge pull request #​795 from lamweili/code-coverage a225e95
• Merge pull request #​794 from lamweili/migrate-cov fa129dc
• test(#​767): 100% code coverage 9c5bd92
• ci: migrated code coverage from coveralls to codecov 46e6feb
• feat: supports http2 da57804
• Merge pull request #​767 from alexandre-abrioux/expect-stacktrace e064b5a
• Merge pull request #​774 from jmccure/update-promise-example-readme ba4b43b
• Merge pull request #​792 from lamweili/refactor/test b8c2e29
• ci: added ci da1e842
• refactor(test): do not hardcode any ports, use ephemeral ports 8847310
• refactor(test): do not have both s and server, renamed to server for consistency c1c4402
• test: 100% test coverage 8bf4c14
• refactor(TestAgent): removed the host param when creating Test object 1c8930d
• feat(TestAgent): decoupled TestAgent and superagent's Agent to support more than ca, key, cert 5e23869
• fix(TestAgent): attach cookies to agent after plugin is used 6d9b9cb
• Update promise example to work with Mocha 5862fe6
• fix: add stacktrace to failed expect function call 3dba4e9
• test: add failing test b24da85

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