Fix: Look for a known filename produced by webpack.

Author: bjones1

runestone/__main__.py

@@ -150,8 +150,8 @@ def build(all, wd):
     else:
         os.chdir(findProjectRoot())
     sys.path.insert(0, os.getcwd())
-    if not pathlib.Path(resource_filename("runestone", "dist/runestone.bundle.js")).exists():
-        click.echo("Error -- You are missing runestone.bundle.js.  Please make sure")
+    if not pathlib.Path(resource_filename("runestone", "dist/webpack_static_imports.json")).exists():
+        click.echo("Error -- you are missing webpack_static_imports.json.  Please make sure")
         click.echo("you have Runestone installed correctly.")
         click.echo("In a development environment, execute npm run build.")
         sys.exit(-1)