Remove NPM version requirement (#83)

This is causing my docker builds to fail intermittently because the
version of NPM there no longer matches this regex. There isn't any major
reason for this to be required so I am just removing it here to get over
that issue.

package.json

@@ -1,11 +1,10 @@
 {
   "name": "parse-mockdb",
-  "version": "0.2.4",
+  "version": "0.2.5",
   "description": "Parse JS SDK Mocked Database",
   "main": "src/parse-mockdb.js",
   "engines": {
-    "node": ">=5.0.0",
-    "npm": "5.3.x"
+    "node": ">=5.0.0"
   },
   "scripts": {
     "test": "npm run lint && mocha ./test/test",