[Security] Bump sshpk from 1.13.1 to 1.15.1

[dependabot-preview]

Bumps sshpk from 1.13.1 to 1.15.1. This update includes security fixes.

Vulnerabilities fixed

Sourced from The Sonatype OSS Index.

CWE-400: Uncontrolled Resource Consumption ('Resource Exhaustion')
The software does not properly restrict the size or amount of resources that are requested or influenced by an actor, which can be used to consume more resources than intended.

Affected versions: <1.14.1

Sourced from The GitHub Vulnerability Alert Database.

CVE-2018-3737
See https://nvd.nist.gov/vuln/detail/CVE-2018-3737.

Affected versions: < 1.13.2

Sourced from The Node Security Working Group.

Denial of Service
sshpk is vulnerable to ReDoS when parsing crafted invalid public keys

Affected versions: <=1.13.1

Release notes

Sourced from sshpk's releases.

v1.14.1

• Remove all remaining usage of jodid25519 (abandoned dep)
• Add support for DNSSEC key format
• Add support for Ed25519 keys in PEM format (according to draft-curdle-pkix)
• Fixes for X.509 encoding issues (asn.1 NULLs in RSA certs, cert string type mangling)
• Performance issues parsing long SSH public keys

Commits

• 2ab4f2a md5 fingerprints not quite right TritonDataCenter/node-sshpk#56 md5 fingerprints not quite right
• 026ef47 stop using optional deps to fix webpack TritonDataCenter/node-sshpk#53 stop using optional deps to fix webpack
• 53e23fe Support PKCS#5 AES-256-CBC encrypted private keys TritonDataCenter/node-sshpk#50 Support PKCS#5 AES-256-CBC encrypted private keys
• 6b68d49 want API for accessing x509 extensions TritonDataCenter/node-sshpk#54 want API for accessing x509 extensions
• 1088992 Buffer no longer performs length check for hex strings in node v8.x  TritonDataCenter/node-sshpk#52 Buffer no longer performs length check for hex strings i...
• 6ec6f9d want support for more obscure DN OIDs TritonDataCenter/node-sshpk#38 want support for more obscure DN OIDs
• 1cc4c99 package.json repository does not point to Joyent TritonDataCenter/node-sshpk#51 package.json repository does not point to Joyent
• 175758a Use Buffer.(from|alloc) instead of deprecated Buffer API TritonDataCenter/node-sshpk#46 Use Buffer.(from|alloc) instead of deprecated Buffer API
• 6edb37c Release 1.14.0
• 46065d3 Performance issues parsing long SSH public keys TritonDataCenter/node-sshpk#44 Performance issues parsing long SSH public keys
• Additional commits viewable in compare view

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