fix: IE10 compatibility (#691)

* fix: IE10 compatibility

* chore: use built-in helper fn

Author: cheng-kang

Diff for: src/core/render/compiler.js

@@ -241,7 +241,7 @@ export class Compiler {
         }
         href = router.toURL(href, null, router.getCurrentPath())
       } else {
-        attrs += href.startsWith('mailto:') ? '' : ` target="${linkTarget}"`
+        attrs += href.indexOf('mailto:') === 0 ? '' : ` target="${linkTarget}"`
       }
 
       if (config.target) {

Diff for: src/plugins/search/search.js

@@ -16,7 +16,7 @@ function escapeHtml(string) {
 function getAllPaths(router) {
   const paths = []
 
-  document.querySelectorAll('.sidebar-nav a:not(.section-link):not([data-nosearch])').forEach(node => {
+  Docsify.dom.findAll('.sidebar-nav a:not(.section-link):not([data-nosearch])').forEach(node => {
     const href = node.href
     const originHref = node.getAttribute('href')
     const path = router.parse(href).path