chore(deps): update nest monorepo to v6.8.0 (#93)

Author: renovate[bot]

package-lock.json

@@ -20,9 +20,9 @@
     "semantic-release": "semantic-release"
   },
   "devDependencies": {
-    "@nestjs/common": "6.7.2",
-    "@nestjs/core": "6.7.2",
-    "@nestjs/testing": "6.7.2",
+    "@nestjs/common": "6.8.0",
+    "@nestjs/core": "6.8.0",
+    "@nestjs/testing": "6.8.0",
     "rxjs": "6.5.3",
     "@semantic-release/changelog": "3.0.4",
     "@types/jest": "24.0.18",