sync up api image handler filter with ExportContainer

- Closes #331

api/handlers/image.js

@@ -16,6 +16,12 @@ module.exports = browser => async (req, res) => {
 
     const targetElement = await page.$('.export-container')
 
+    targetElement.querySelectorAll('span[role="presentation"]').forEach(node => {
+      if (node.innerText && node.innerText.match(/%\d\S/)) {
+        node.innerText = encodeURIComponent(node.innerText)
+      }
+    })
+
     const dataUrl = await page.evaluate((target = document) => {
       const config = {
         style: {
@@ -23,15 +29,6 @@ module.exports = browser => async (req, res) => {
           'transform-origin': 'center'
         },
         filter: n => {
-          // %[00 -> 19] cause failures
-          if (
-            n.innerText &&
-            n.innerText.match(/%\S\S/) &&
-            n.className &&
-            n.className.startsWith('cm-') // is CodeMirror primitive string
-          ) {
-            n.innerText = encodeURIComponent(n.innerText)
-          }
           if (n.className) {
             return String(n.className).indexOf('eliminateOnRender') < 0
           }