Lock minor version of selenium

Webdriver logs in actual version of selenium should never be instantiated directly:
https://github.com/SeleniumHQ/selenium/blob/fa5ac92b451cff497e686d8e1e67c9c3101440a3/javascript/node/selenium-webdriver/lib/webdriver.js#L1429-L1432

But drool still uses selenium 2.46.1:
https://github.com/samccone/drool/commit/3770a157d218e6ea27ef9fd2e78f58105375fca0

So the fast fix is the old version of selenium.

Fixes #1605.

tests/package.json

@@ -7,7 +7,7 @@
     "mocha": "*",
     "mocha-known-issues-reporter": "git+https://github.com/ColinEberhardt/mocha-known-issues-reporter.git#v0.0.0",
     "optimist": "^0.6.1",
-    "selenium-webdriver": "^2.46.1",
+    "selenium-webdriver": "~2.46.1",
     "drool": "0.2.2"
   },
   "scripts": {