add missing quotes

Fix launch.json formatting error caused by missing quotes

Change-Id: Id94bf99c99e765abbe70a28eddf54947ce552c63
GitHub-Last-Rev: 224e7d0f0e2530a4fe0970c5a468a0ba28ee3898
GitHub-Pull-Request: golang/vscode-go#2678
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/470115
Reviewed-by: Suzy Mueller <suzmue@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/docs/debugging.md b/docs/debugging.md
index 70baee0..71f3306 100644
--- a/docs/debugging.md
+++ b/docs/debugging.md
@@ -843,7 +843,7 @@
     "port": 12345,
     "host": "127.0.0.1", // can skip for localhost
     "substitutePath": [
-      { "from": ${workspaceFolder}, "to": "/path/to/remote/workspace" },
+      { "from": "${workspaceFolder}", "to": "/path/to/remote/workspace" },
       ...
   ]
 }