content: update Twitter username shurcooL to dmitshur

I have renamed my GitHub username from shurcooL to dmitshur.
Update the link in the Contribution Workshop article to point
to the new username.

Reference: https://twitter.com/dmitshur/status/1021266582834634752.

Change-Id: I5562f8534ba1b67ea7981ea46287d66601611dfe
Reviewed-on: https://go-review.googlesource.com/125440
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/content/contributor-workshop.article b/content/contributor-workshop.article
index 60c2724..a0a999d 100644
--- a/content/contributor-workshop.article
+++ b/content/contributor-workshop.article
@@ -304,7 +304,7 @@
 
 ** My Mentorship Experience
 
-by [[https://twitter.com/shurcooL][Dmitri]]
+by [[https://twitter.com/dmitshur][Dmitri]]
 
 I was looking forward to participating in the Contribution Workshop event as a
 mentor. I had high expectations for the event, and thought it was a great idea