fix(zipper): add ‘use strict’ to exampleZipper.js (#3327)

To beat error “SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode”

tools/example-zipper/exampleZipper.js

@@ -1,3 +1,5 @@
+'use strict';
+
 // Canonical path provides a consistent path (i.e. always forward slashes) across different OSes
 var path = require('canonical-path');
 var jsonfile = require('jsonfile');