Move html5-validator to devDependencies

html5-validator is only used for testing the master server web interface
and does not need to be included on production installs.

package.json

@@ -39,7 +39,6 @@
     "follow-redirects": "^1.5.0",
     "fs-extra": "^6.0.1",
     "getmac": "^1.4.0",
-    "html5-validator": "^1.0.7",
     "ini": "^1.3.5",
     "jsonwebtoken": "^8.2.1",
     "lib": "file:./lib",
@@ -69,6 +68,7 @@
     "underscore": "^1.8.3"
   },
   "devDependencies": {
+    "html5-validator": "^1.0.7",
     "istanbul": "^0.4.5",
     "mocha": "^3.5.3",
     "mocha-sinon": "^2.0.0",