Bump semver and nsp in /generator-exercise

Bumps [semver](https://github.com/npm/node-semver) to 5.7.2 and updates ancestor dependency [nsp](https://github.com/nodesecurity/nsp). These dependencies need to be updated together.


Updates `semver` from 5.4.1 to 5.7.2
- [Release notes](https://github.com/npm/node-semver/releases)
- [Changelog](https://github.com/npm/node-semver/blob/v5.7.2/CHANGELOG.md)
- [Commits](npm/node-semver@v5.4.1...v5.7.2)

Updates `nsp` from 2.7.0 to 3.2.1
- [Commits](nodesecurity/nsp@v2.7.0...v3.2.1)

---
updated-dependencies:
- dependency-name: semver
  dependency-type: indirect
- dependency-name: nsp
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

generator-exercise/package-lock.json

@@ -19,7 +19,7 @@
   "devDependencies": {
     "yeoman-test": "^1.6.0",
     "yeoman-assert": "^3.0.0",
-    "nsp": "^2.6.3",
+    "nsp": "^3.2.1",
     "eslint": "^4.1.0",
     "eslint-config-xo-space": "^0.16.0",
     "jest": "^19.0.2",