30% faster

If regex is so fast that it's worth using at the beginning of the function, why not use it for the stepping?

```
regex stepping x 280 ops/sec ±0.41% (83 runs sampled)
original x 214 ops/sec ±0.60% (85 runs sampled)
```

index.js

@@ -13,7 +13,7 @@
  * @private
  */
 
-var matchHtmlRegExp = /["'&<>]/
+var matchHtmlRegExp = /["'&<>]/g
 
 /**
  * Module exports.
@@ -30,21 +30,14 @@ module.exports = escapeHtml
  * @public
  */
 
-function escapeHtml (string) {
-  var str = '' + string
-  var match = matchHtmlRegExp.exec(str)
-
-  if (!match) {
-    return str
-  }
-
-  var escape
-  var html = ''
-  var index = 0
+function escapeHtml (str) {
   var lastIndex = 0
+  var html = ''
+  var escape = ''
+  var match
 
-  for (index = match.index; index < str.length; index++) {
-    switch (str.charCodeAt(index)) {
+  while (match = matchHtmlRegExp.exec(str)) {
+    switch (str.charCodeAt(match.index)) {
       case 34: // "
         escape = '&quot;'
         break
@@ -60,19 +53,10 @@ function escapeHtml (string) {
       case 62: // >
         escape = '&gt;'
         break
-      default:
-        continue
     }
-
-    if (lastIndex !== index) {
-      html += str.substring(lastIndex, index)
-    }
-
-    lastIndex = index + 1
+    html += str.substring(lastIndex, match.index)
+    lastIndex = match.index + 1
     html += escape
   }
-
-  return lastIndex !== index
-    ? html + str.substring(lastIndex, index)
-    : html
+  return html + str.substring(lastIndex)
 }