writing_a_great_proposol.md: Update_GSOC_link

Changes the old broken link with the new link to
summerofcode.withgoogle.com

Closes #642

_faq/writing-a-great-proposal.md

@@ -25,4 +25,4 @@ Please follow the **application template** in the faq. All fields are required i
 
 For writing your proposal we recommend using [Google Docs](https://www.google.com/docs/about/) as this will be supported by the Google submission system.
 
-If needed, you can get further information about GSoC [here](http://write.flossmanuals.net/gsocstudentguide/what-is-google-summer-of-code/).
+If needed, you can get further information about GSoC [here](https://summerofcode.withgoogle.com/).