Use 2018 as target for extensions since we are now running on node 10

extensions/shared.tsconfig.json

 {
 	"compilerOptions": {
-		"target": "es2017",
+		"target": "es2018",
 		"module": "commonjs",
-		"lib": [
-			"es6",
-			"es2015.promise"
-		],
 		"strict": true,
 		"alwaysStrict": true,
 		"noImplicitAny": true,

extensions/typescript-language-features/src/features/bufferSyncSupport.ts

@@ -157,8 +157,7 @@ class GetErrRequest {
 		};
 
 		client.executeAsync('geterr', args, _token.token)
-			.catch(() => true)
-			.then(() => {
+			.finally(() => {
 				if (this._done) {
 					return;
 				}