launch.json: disable other extensions

When running Launch Extension, disable other extensions (e.g. golang.go)
which will conflict with golang.go-nightly.

Change-Id: Ic983e3431d4a3fca62a6a5ab8e041c6a6d0a3a15
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/237681
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

Author: hyangah

.vscode/launch.json

@@ -9,7 +9,8 @@
 			// path to VSCode executable
 			"runtimeExecutable": "${execPath}",
 			"args": [
-				"--extensionDevelopmentPath=${workspaceFolder}"
+				"--extensionDevelopmentPath=${workspaceFolder}",
+				"--disable-extensions"
 			],
 			"stopOnEntry": false,
 			"sourceMaps": true,