Update verify_build.py

Author: dclong

verify_build.py

@@ -5,4 +5,4 @@
 
 paths = [str(path) for path in BASE_DIR.glob("*.sh") if path.name not in EXCLUDE and not path.with_suffix(".tar.gz").is_file()]
 if paths:
-    raise FileNotFoundError(f"The following environment(s) failed to build:\n{''.join(paths)}")
+    raise FileNotFoundError(f"The following environment(s) failed to build:\n{' '.join(paths)}")