Prepare release v0.4 (#255)

Author: kvaps

site/content/en/docs/v0.3/_index.md renamed to site/content/en/docs/v0.4/_index.md

@@ -1,9 +1,9 @@
 ---
-title: v0.3 docs
+title: v0.4 docs
 cascade:
-  version: v0.3
-  versName: &name v0.3
-  git_version_tag: v0.3
+  version: v0.4
+  versName: &name v0.4
+  git_version_tag: v0.4
   exclude_search: false
 linkTitle: *name
 simple_list: true

site/content/en/docs/v0.3/contribution-guidelines/_index.md renamed to site/content/en/docs/v0.4/contribution-guidelines/_index.md

@@ -53,11 +53,11 @@ params:
 
   version_menu: Releases
   archived_version: false
-  version: v0.3
+  version: v0.4
   url_latest_version: https://etcd.aenix.io/docs/latest
   versions:
-    - version: v0.3
-      url: https://etcd.aenix.io/docs/v0.3
+    - version: v0.4
+      url: https://etcd.aenix.io/docs/v0.4
 
   copyright:
     authors: "Aenix.io | "