fix: move selenium to development deps (#55)

* fix: move selenium to development deps

Since we list it as a peerDependency, there's no reason to additionally list it as a regular dependency.

This fixes some warnings output by Yarn.

Author: stephenmathieson

package-lock.json

@@ -60,11 +60,11 @@
     "istanbul": "^0.4.5",
     "mocha": "^3.1.2",
     "proxyquire": "^1.5.0",
+    "selenium-webdriver": "^2.53.3",
     "serve-static": "^1.9.3",
     "sinon": "^1.17.3"
   },
   "dependencies": {
-    "axe-core": "^3.0.0",
-    "selenium-webdriver": ">= 2.53.1"
+    "axe-core": "^3.0.0"
   }
 }