Update version number for docker installation (#853)

Author: Erik Bledsoe

setup/docker.md

@@ -36,7 +36,7 @@ Coder requires x86-64 and does not support ARM-based processors at this time.
       -p 7080:7080 \
       -v /var/run/docker.sock:/var/run/docker.sock \
       -v ~/.coder:/var/run/coder \
-      codercom/coder:1.27.0
+      codercom/coder:1.28.0
    ```
 
    When this process is complete, Coder will print the URL you can use to access