src/goInstallTools.ts: return a rejected promise when go isn't found

If Go is not found, return a rejected promise, so, the promise
chaining can work. updateGoVarsFromConfig is not declared as an
async, so returning nothing means returning nothing.

Fixes golang/vscode-go#660

Change-Id: I16f73ca057f3b6bb220a754afc1baa43cc891c22
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/255963
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>
diff --git a/src/goInstallTools.ts b/src/goInstallTools.ts
index 3ca1538..63856fc 100644
--- a/src/goInstallTools.ts
+++ b/src/goInstallTools.ts
@@ -349,7 +349,7 @@
 	logVerbose(`updateGoVarsFromConfig: found 'go' in ${goRuntimePath}`);
 	if (!goRuntimePath) {
 		suggestDownloadGo();
-		return;
+		return Promise.reject();
 	}
 
 	return new Promise<void>((resolve, reject) => {
@@ -486,7 +486,7 @@
 	}
 
 	const choice = await vscode.window.showErrorMessage(
-		`Failed to find the "go" binary in either GOROOT(${getCurrentGoRoot()}) or PATH(${envPath}. ` +
+		`Failed to find the "go" binary in either GOROOT(${getCurrentGoRoot()}) or PATH(${envPath}). ` +
 		`Check PATH, or Install Go and reload the window.`,
 		'Go to Download Page'
 	);