fix: fixed activity graph URL

More info is
[here](Ashutosh00710/github-readme-activity-graph#197 (comment))

Signed-off-by: Vikas Kumar <vikas.kumar@eptura.com>

README.md

@@ -30,7 +30,7 @@
 <br/>
 <br/>
 
-<a href="https://github.com/vikas027/github-readme-activity-graph"><img alt="vikas027's Activity Graph" src="https://activity-graph.herokuapp.com/graph?username=vikas027&bg_color=0D1117&color=5BCDEC&line=5BCDEC&point=FFFFFF&hide_border=true" /></a>
+<a href="https://github.com/vikas027/github-readme-activity-graph"><img alt="vikas027's Activity Graph" src="https://github-readme-activity-graph.vercel.app/graph?username=vikas027&bg_color=0D1117&color=5BCDEC&line=5BCDEC&point=FFFFFF&hide_border=true" /></a>
 
 ![Github Trophy](https://github-profile-trophy.vercel.app/?username=vikas027)