refactor for coding style

lib/components/leaf.js

@@ -127,10 +127,12 @@ class Leaf extends React.Component {
     })
 
     const style = marks.reduce((memo, mark) => {
-      const renderedMark = renderMark(mark, marks)
-      Object.keys(renderedMark).forEach((k) => {
-        memo[k] = renderedMark[k]
-      })
+      const styles = renderMark(mark, marks)
+
+      for (const key in styles) {
+        memo[key] = styles[key]
+      }
+
       return memo
     }, {})