doc/npm.md: Fix formatting

nhooyr · nhooyr · commit 6c67dc7ce1b7 · 2020-12-04T02:34:18.000-05:00
diff --git a/doc/npm.md b/doc/npm.md
@@ -36,6 +36,7 @@ npm config set python python2
 ```
 
 ## macOS
+
 ```bash
 xcode-select --install
 ```
