Fix search query: filter out w3schools by url

To filter out w3schools adequately, "-inurl:w3schools.com" should be used instead of simply "-w3schools". Likely you meant to block the url, not all websites referring to w3school in their content. Like w3fools.com...

Example:

* **query**: w3fools -w3schools
  **result**: w3fools.com is filtered out (not what you want)

* **query**: w3fools -inurl:w3schools.com
  **result**: w3fools.com is the first result

_Note: not tested against all available search engines, obviously. It works for Google, Yahoo and Bing, for starters._