fix: trimXXX的polyfill

src/polyfill.js

 /* eslint-disable no-extend-native */
 import '@babel/polyfill';
 
-String.prototype.trimStart = String.prototype.trimStart ? String.prototype.trimStart : function trimStart() {
-  if (String.prototype.trimLeft) {
-    return this.trimLeft();
-  } else if (String.prototype.trim) {
+String.prototype.trimLeft = String.prototype.trimLeft ? String.prototype.trimLeft : function trimLeft() {
   const trimmed = this.trim();
   const indexOfWord = this.indexOf(trimmed);
   return this.slice(indexOfWord, this.length);
-  }
 };
 
-String.prototype.trimLeft = String.prototype.trimLeft ? String.prototype.trimLeft : String.prototype.trimStart;
+String.prototype.trimStart = String.prototype.trimStart ? String.prototype.trimStart : String.prototype.trimLeft;
 
-String.prototype.trimEnd = String.prototype.trimEnd ? String.prototype.trimEnd : function trimEnd() {
-  if (String.prototype.trimRight) {
-    return this.trimRight();
-  } else if (String.prototype.trim) {
+String.prototype.trimRight = String.prototype.trimRight ? String.prototype.trimRight : function trimRight() {
   const trimmed = this.trim();
   const indexOfWord = this.indexOf(trimmed);
   return this.slice(0, indexOfWord + trimmed.length);
-  }
 };
 
-String.prototype.trimRight = String.prototype.trimRight ? String.prototype.trimRight : String.prototype.trimEnd;
+String.prototype.trimEnd = String.prototype.trimEnd ? String.prototype.trimEnd : String.prototype.trimRight;