Add ?module support for HTML files

Closes #113

modules/actions/serveJavaScriptModule.js

@@ -1,35 +1,9 @@
 const etag = require("etag");
-const babel = require("babel-core");
 
 const getContentTypeHeader = require("../utils/getContentTypeHeader");
-const unpkgRewrite = require("../plugins/unpkgRewrite");
-
-function rewriteBareModuleIdentifiers(code, packageConfig) {
-  const dependencies = Object.assign(
-    {},
-    packageConfig.peerDependencies,
-    packageConfig.dependencies
-  );
-
-  const options = {
-    // Ignore .babelrc and package.json babel config
-    // because we haven't installed dependencies so
-    // we can't load plugins; see #84
-    babelrc: false,
-    plugins: [unpkgRewrite(dependencies)]
-  };
-
-  return babel.transform(code, options).code;
-}
+const rewriteBareModuleIdentifiers = require("../utils/rewriteBareModuleIdentifiers");
 
 function serveJavaScriptModule(req, res) {
-  if (req.entry.contentType !== "application/javascript") {
-    return res
-      .status(403)
-      .type("text")
-      .send("?module mode is available only for JavaScript files");
-  }
-
   try {
     const code = rewriteBareModuleIdentifiers(
       req.entry.content.toString("utf8"),