Use unitless lineheights.

Fixes #571.

Author: jasmussen

editor/assets/stylesheets/_variables.scss

@@ -33,11 +33,11 @@ $blue-medium-100: #E5F5FA;
 /* Other */
 $default-font: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Oxygen-Sans,Ubuntu,Cantarell,"Helvetica Neue",sans-serif;
 $default-font-size: 13px;
-$default-line-height: 1.4em;
+$default-line-height: 1.4;
 $editor-font: "Noto Serif", serif;
 $editor-html-font: Menlo, Consolas, monaco, monospace;
 $editor-font-size: 16px;
-$editor-line-height: 1.8em;
+$editor-line-height: 1.8;
 $item-spacing: 10px;
 $header-height: 56px;
 $sidebar-width: 320px;