Don't show scrollbars when not needed for the completion item documentation

Author: krassowski

packages/completion-theme/style/index.css

@@ -16,3 +16,10 @@
   display: flex;
   justify-content: space-between;
 }
+
+/* a workaround for scrollbars being always on in the completer documentation panel, see
+ https://github.com/krassowski/jupyterlab-lsp/pull/322#issuecomment-682724175
+ */
+.jp-Completer-docpanel {
+  overflow: auto;
+}