Replace "Object.assign" (not support in IE) by "util/extend"

lib/handlebars/compiler/compiler.js

@@ -1,7 +1,7 @@
 /* eslint-disable new-cap */
 
 import Exception from '../exception';
-import {isArray, indexOf} from '../utils';
+import {isArray, indexOf, extend} from '../utils';
 import AST from './ast';
 
 const slice = [].slice;
@@ -488,7 +488,7 @@ export function compile(input, options = {}, env) {
     throw new Exception('You must pass a string or Handlebars AST to Handlebars.compile. You passed ' + input);
   }
 
-  options = Object.assign({}, options);
+  options = extend({}, options);
   if (!('data' in options)) {
     options.data = true;
   }