readme: force update image of contributors

Author: love-linger

README.md

@@ -91,5 +91,5 @@ This app supports open repository in external tools listed in the table below.
 Thanks to all the people who contribute.
 
 <a href="https://github.com/sourcegit-scm/sourcegit/graphs/contributors">
-  <img src="https://contrib.rocks/image?repo=sourcegit-scm/sourcegit&columns=10&t=3" />
+  <img src="https://contrib.rocks/image?repo=sourcegit-scm/sourcegit&columns=10&t=4" />
 </a>