add missing dependency

Author: Fabio Folchi

package.json

@@ -1,6 +1,6 @@
 {
   "name": "monk-log",
-  "version": "3.0.1",
+  "version": "3.1.0",
   "private": false,
   "engines": {
     "node": ">=8.3.0"
@@ -21,6 +21,7 @@
   "author": "Monk Software",
   "license": "ISC",
   "dependencies": {
+    "@types/loglevel": "^1.5.4",
     "chalk": "^2.4.2",
     "loglevel": "^1.6.1",
     "loglevel-plugin-prefix": "^0.8.4"