workaround Safari quirks (#4314)

fixes #1753

lib/minify.js

@@ -89,6 +89,7 @@ function minify(files, options) {
             toplevel: false,
             validate: false,
             warnings: false,
+            webkit: false,
             wrap: false,
         }, true);
         if (options.validate) AST_Node.enable_validation();
@@ -101,6 +102,7 @@ function minify(files, options) {
         set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
         set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
         set_shorthand("toplevel", options, [ "compress", "mangle" ]);
+        set_shorthand("webkit", options, [ "mangle", "output" ]);
         var quoted_props;
         if (options.mangle) {
             options.mangle = defaults(options.mangle, {
@@ -111,6 +113,7 @@ function minify(files, options) {
                 properties: false,
                 reserved: [],
                 toplevel: false,
+                webkit: false,
             }, true);
             if (options.mangle.properties) {
                 if (typeof options.mangle.properties != "object") {