[website] Update docker version for 0.7.0 RC4

Author: wuchong

website/fluss-versions.json

@@ -9,7 +9,7 @@
     "versionName": "version-0.7",
     "fullVersion": "0.7.0",
     "shortVersion": "0.7",
-    "dockerVersion": "v0.7.0-rc3"
+    "dockerVersion": "v0.7.0-rc4"
   },
   {
     "versionName": "version-0.6",