tests: Enable 'npm run selenium' on Windows

Run the script explictly via sh, the default is cmd.exe on Windows.
Also ported from bash to sh per Jforrester's request.

Change-Id: I96b66c6ae01a1761619955be2e8a3dbc64edff18

package.json

@@ -8,7 +8,7 @@
     "qunit": "grunt qunit",
     "doc": "jsduck",
     "postdoc": "grunt copy:jsduck",
-    "selenium": "./tests/selenium/selenium.sh",
+    "selenium": "sh ./tests/selenium/selenium.sh",
     "selenium-daily": "npm run selenium-test -- --mochaOpts.grep @daily",
     "selenium-test": "wdio ./tests/selenium/wdio.conf.js"
   },

tests/selenium/selenium.sh

@@ -1,4 +1,5 @@
-#!/usr/bin/env bash
+# Called via "npm run selenium", see /package.json.
+
 set -euo pipefail
 
 # Manually check if chromedriver is installed and let it fail early with a descriptive