manager: Make graph tree more tall than wide

Helps with readability.

techtree-manager/src/tree.rs

@@ -160,12 +160,17 @@ impl Tree {
                 petgraph::dot::Config::EdgeNoLabel,
                 petgraph::dot::Config::NodeNoLabel,
                 petgraph::dot::Config::RankDir(petgraph::dot::RankDir::BT),
+                petgraph::dot::Config::GraphContentOnly,
             ],
             &|_g, _edge_id| "".to_string(),
             &|_g, (_, element)| element.to_dot_node_attributes(None),
         );
 
-        format!("{:?}", dot)
+        format!(r#"digraph {{
+    ranksep=1.2
+{:?}
+}}
+"#, dot)
     }
 
     pub fn to_mermaid(&self, repo_url: &str) -> String {