fix: add var printWarning = to comply with ES5 strict mode

whtsky · web-flow · commit 677dcfab1a23 · 2018-05-29T09:48:03.000+08:00
close #25
diff --git a/warning.js b/warning.js
@@ -21,7 +21,7 @@ var __DEV__ = process.env.NODE_ENV !== 'production';
 var warning = function() {};
 
 if (__DEV__) {
-  function printWarning(format, args) {
+  var printWarning = function printWarning(format, args) {
     var len = arguments.length;
     args = new Array(len > 2 ? len - 2 : 0);
     for (var key = 2; key < len; key++) {
