Upgrade 'std/esm' to 'esm', fixing the build issues on Node 10

(closes #5028, re: a065f2f2)

'std/esm' has been replaced with just 'esm'
This fixes the build for Node 10 and we can return to using
the current version now that we've dropped support for Node 4

development_server.js

@@ -12,9 +12,9 @@ var buildSrc = require('./build_src')(isDevelopment);
 var buildCSS = require('./build_css')(isDevelopment);
 
 buildData()
-.then(function () {
-    return buildSrc();
-});
+    .then(function () {
+        return buildSrc();
+    });
 
 buildCSS();