Bump ejs, yeoman-generator and yeoman-test in /generator-exercise

Bumps [ejs](https://github.com/mde/ejs) to 3.1.9 and updates ancestor dependencies [ejs](https://github.com/mde/ejs), [yeoman-generator](https://github.com/yeoman/generator) and [yeoman-test](https://github.com/yeoman/yeoman-test). These dependencies need to be updated together.


Updates `ejs` from 2.5.7 to 3.1.9
- [Release notes](https://github.com/mde/ejs/releases)
- [Commits](https://github.com/mde/ejs/compare/v2.5.7...v3.1.9)

Updates `yeoman-generator` from 1.1.1 to 5.8.0
- [Release notes](https://github.com/yeoman/generator/releases)
- [Commits](https://github.com/yeoman/generator/compare/v1.1.1...v5.8.0)

Updates `yeoman-test` from 1.7.0 to 7.4.0
- [Release notes](https://github.com/yeoman/yeoman-test/releases)
- [Commits](https://github.com/yeoman/yeoman-test/compare/v1.7.0...v7.4.0)

---
updated-dependencies:
- dependency-name: ejs
  dependency-type: indirect
- dependency-name: yeoman-generator
  dependency-type: direct:production
- dependency-name: yeoman-test
  dependency-type: direct:development
...

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

generator-exercise/package.json

@@ -17,7 +17,7 @@
     "yeoman-generator"
   ],
   "devDependencies": {
-    "yeoman-test": "^1.6.0",
+    "yeoman-test": "^7.4.0",
     "yeoman-assert": "^3.0.0",
     "nsp": "^2.6.3",
     "eslint": "^4.1.0",
@@ -28,7 +28,7 @@
   "dependencies": {
     "chalk": "^1.1.3",
     "extend": "^3.0.2",
-    "yeoman-generator": "^1.0.0",
+    "yeoman-generator": "^5.8.0",
     "yosay": "^2.0.0"
   },
   "jest": {