_content/solutions: update dropbox blog link

dropbox blog url was changed.
https://dropbox.tech/infrastructure/open-sourcing-our-go-libraries

Change-Id: Ide5b82ab1283d74bf3346590fa9344b7fd0b4dc3
Reviewed-on: https://go-review.googlesource.com/c/website/+/711680
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: vinaykulk621

_content/solutions/dropbox.md

@@ -5,6 +5,6 @@ company: Dropbox
 logoSrc: dropbox.png
 logoSrcDark: dropbox.png
 series: Case Studies
-link: https://blogs.dropbox.com/tech/2014/07/open-sourcing-our-go-libraries/
+link: https://dropbox.tech/infrastructure/open-sourcing-our-go-libraries
 inLandingPageGrid: true
 ---