Bump semver from 5.4.1 to 6.1.0 in /terminus-plugin-manager

Bumps [semver](https://github.com/npm/node-semver) from 5.4.1 to 6.1.0.
- [Release notes](https://github.com/npm/node-semver/releases)
- [Changelog](https://github.com/npm/node-semver/blob/master/CHANGELOG.md)
- [Commits](https://github.com/npm/node-semver/compare/v5.4.1...v6.1.0)

terminus-plugin-manager/package.json

@@ -23,7 +23,7 @@
     "@types/webpack-env": "1.13.0",
     "css-loader": "^0.28.0",
     "ngx-pipes": "^1.6.1",
-    "semver": "^5.3.0"
+    "semver": "^6.1.0"
   },
   "peerDependencies": {
     "@angular/common": "4.0.1",