Update dependency helmet to v3

[mend-for-github-com]

This PR contains the following updates:

Package	Type	Update	Change
helmet (source)	dependencies	major	^2.0.0 → ^3.0.0

By merging this PR, the issue #16 will be automatically resolved and closed:

Severity	CVSS Score	Vulnerability	Reachability
Medium	4.3	CVE-2017-20162
Low	3.5	CVE-2017-20165

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Release Notes

helmetjs/helmet (helmet)

v3.8.2

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Changed

• Updated connect dependency to latest

v3.8.1

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Fixed

• csp does not automatically set report-to when setting report-uri

v3.8.0

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Changed

• hsts no longer cares whether it's HTTPS and always sets the header

v3.7.0

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Added

• csp now supports report-to directive

Changed

• Throw an error when used incorrectly
• Add a few documentation files to npmignore

v3.6.1

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Changed

• Bump connect version

v3.6.0

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Added

• expectCt middleware for setting the Expect-CT header

v3.5.0

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Added

• csp now supports the worker-src directive

v3.4.1

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Changed

• Bump connect version

v3.4.0

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Added

• csp now supports more sandbox directives

v3.3.0

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Added

• referrerPolicy allows strict-origin and strict-origin-when-cross-origin directives

Changed

• Bump connect version

v3.2.0

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Added

• csp now allows manifest-src directive

v3.1.0

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Added

• csp now allows frame-src directive

v3.0.0

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Changed

• csp will check your directives for common mistakes and throw errors if it finds them. This can be disabled with loose: true.
• Empty arrays are no longer allowed in csp. For source lists (like script-src or object-src), use the standard scriptSrc: ["'none'"]. The sandbox directive can be sandbox: true to block everything.
• false can disable a CSP directive. For example, scriptSrc: false is the same as not specifying it.
• In CSP, reportOnly: true no longer requires a report-uri to be set.
• hsts's maxAge now defaults to 180 days (instead of 1 day)
• hsts's maxAge parameter is seconds, not milliseconds
• hsts includes subdomains by default
• domain parameter in frameguard cannot be empty

Removed

• noEtag option no longer present in noCache
• iOS Chrome connect-src workaround in CSP module

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