Merge pull request #844 from nushell/unknown-value

Rename <unknown> to <value>

src/format/table.rs

@@ -42,7 +42,7 @@ impl TableView {
         let mut headers = TableView::merge_descriptors(values);
 
         if headers.len() == 0 {
-            headers.push("<unknown>".to_string());
+            headers.push("<value>".to_string());
         }
 
         let mut entries = vec![];