feat(node): add SVN (#426)

* Add: SVN

* updated the png file to remove the green background as suggested by gabriel-tessier

diagrams/onprem/vcs.py

@@ -24,4 +24,8 @@ class Gitlab(_Vcs):
     _icon = "gitlab.png"
 
 
+class Svn(_Vcs):
+    _icon = "svn.png"
+
+
 # Aliases

docs/nodes/onprem.md

@@ -235,6 +235,7 @@ Node classes list of onprem provider.
 - **diagrams.onprem.vcs.Gitea**
 - **diagrams.onprem.vcs.Github**
 - **diagrams.onprem.vcs.Gitlab**
+- **diagrams.onprem.vcs.Svn**
 
 ## onprem.workflow