Package.json: Bump npm and nodejs

The npm and node versions listed in package.json were too old to
compile. Updated them to match the versions in the README.

If using an older version then these, the webui will still try
to compile but will display a warning message like:

   ╭─────────────────────────────────────╮
   │                                     │
   │   Update available 5.6.0 → 6.4.1    │
   │     Run npm i -g npm to update      │
   │                                     │
   ╰─────────────────────────────────────╯

Change-Id: If7165f80c9344f3bcab92b1399c52925676515bb
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/package.json b/package.json
index 2163f15..9cb77ce 100644
--- a/package.json
+++ b/package.json
@@ -77,8 +77,8 @@
   },
   "license": "MIT",
   "engines": {
-    "node": ">=0.11.13",
-    "npm": ">=1.4.28"
+    "node": ">=4.2.6",
+    "npm": ">=5.6.0"
   },
   "author": ""
 }