Updates CodeStream tracking link

src/ui/welcome/index.html

@@ -535,7 +535,7 @@
                             <h2>Sponsors</h2>
                             <a
                                 title="Try CodeStream"
-                                href="https://codestream.com/?utm_source=vscmarket&utm_medium=banner&utm_campaign=gitlens"
+                                href="https://codestream.com/?utm_source=gitlens_welcome&utm_medium=banner&utm_campaign=gitlens"
                             >
                                 <!-- prettier-ignore-attribute src -->
                                 <img