Add wildcard for submodules; fix existing esm test and add new.

package.json

@@ -25,8 +25,11 @@
     "wrappers/"
   ],
   "exports": {
-    "import": "./mustache.mjs",
-    "require": "./mustache.js"
+    ".": {
+      "import": "./mustache.mjs",
+      "require": "./mustache.js"
+    },
+    "./*": "./*"
   },
   "volo": {
     "url": "https://raw.github.com/janl/mustache.js/{version}/mustache.js"

test/module-systems/esm-test-exports.mjs

@@ -0,0 +1,12 @@
+import assert from 'assert';
+import mustache from 'mustache';
+
+const view = {
+  title: 'Joe',
+  calc: () => 2 + 4
+};
+
+assert.strictEqual(
+  mustache.render('{{title}} spends {{calc}}', view),
+  'Joe spends 6'
+);