add "sync-next-dap" script

Author: weinand

package.json

@@ -4,6 +4,7 @@
 	"license": "MIT",
 	"scripts": {
 		"sync-dap": "curl https://microsoft.github.io/debug-adapter-protocol/debugAdapterProtocol.json > debugProtocol.json && npm run compile",
+		"sync-next-dap": "curl https://raw.githubusercontent.com/microsoft/debug-adapter-protocol/next/debugAdapterProtocol.json > debugProtocol.json && npm run compile",
 		"test": "lerna run test --stream",
 		"compile": "lerna run compile --stream",
 		"version": "lerna version --exact",