[Security] Bump sshpk from 1.13.1 to 1.15.1

Bumps [sshpk](https://github.com/joyent/node-sshpk) from 1.13.1 to 1.15.1. **This update includes security fixes.**
- [Release notes](https://github.com/joyent/node-sshpk/releases)
- [Commits](TritonDataCenter/node-sshpk@v1.13.1...v1.15.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

yarn.lock

@@ -4300,7 +4300,7 @@ safe-regex@^1.1.0:
   dependencies:
     ret "~0.1.10"
 
-"safer-buffer@>= 2.1.2 < 3":
+"safer-buffer@>= 2.1.2 < 3", safer-buffer@^2.0.2:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/safer-buffer/-/safer-buffer-2.1.2.tgz#44fa161b0187b9549dd84bb91802f9bd8385cd6a"
 
@@ -4541,17 +4541,17 @@ sprintf-js@~1.0.2:
   resolved "https://registry.yarnpkg.com/sprintf-js/-/sprintf-js-1.0.3.tgz#04e6926f662895354f3dd015203633b857297e2c"
 
 sshpk@^1.7.0:
-  version "1.13.1"
-  resolved "https://registry.yarnpkg.com/sshpk/-/sshpk-1.13.1.tgz#512df6da6287144316dc4c18fe1cf1d940739be3"
+  version "1.15.1"
+  resolved "https://registry.yarnpkg.com/sshpk/-/sshpk-1.15.1.tgz#b79a089a732e346c6e0714830f36285cd38191a2"
   dependencies:
     asn1 "~0.2.3"
     assert-plus "^1.0.0"
-    dashdash "^1.12.0"
-    getpass "^0.1.1"
-  optionalDependencies:
     bcrypt-pbkdf "^1.0.0"
+    dashdash "^1.12.0"
     ecc-jsbn "~0.1.1"
+    getpass "^0.1.1"
     jsbn "~0.1.0"
+    safer-buffer "^2.0.2"
     tweetnacl "~0.14.0"
 
 stack-utils@^1.0.1: