Update remaining dev-dependencies to latest

Keep should at 8.x for compatibility with connectors.

package.json

@@ -37,12 +37,12 @@
     "@types/node": "^10.0.8",
     "async-iterators": "^0.2.2",
     "bson": "^1.0.4",
-    "coveralls": "^2.13.1",
+    "coveralls": "^3.0.1",
     "eslint": "^4.19.1",
     "eslint-config-loopback": "^10.0.0",
     "loopback-connector-throwing": "file:./test/fixtures/loopback-connector-throwing",
-    "mocha": "^3.2.0",
-    "nyc": "^11.1.0",
+    "mocha": "^5.2.0",
+    "nyc": "^12.0.2",
     "should": "^8.4.0",
     "typescript": "^2.8.3"
   },