Fix tests with the latest version of mocha

umap/static/umap/test/_pre.js

@@ -1,3 +1,6 @@
+window.assert = chai.assert
+window.expect = chai.expect
+
 var qs = function (selector, element) {
   return (element || document).querySelector(selector)
 }

umap/static/umap/test/index.html

@@ -64,8 +64,6 @@
         ignoreLeaks: true,
       })
       chai.config.includeStack = true
-      var assert = chai.assert
-      var expect = chai.expect
     </script>
     <script src="./_pre.js"></script>
     <script src="./Map.js"></script>