src/goInstallTools: use GOROOT/bin for gocode-gomod build too

This should've been done in cl/263977.

Update #757

Change-Id: I51afbc8a2534c1b3f304ba988b6bcec9c944a048
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/264318
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>

Author: hyangah

src/goInstallTools.ts

@@ -241,15 +241,15 @@ export async function installTool(
 
 		// TODO(rstambler): Figure out why this happens and maybe delete it.
 		if (stderr.indexOf('unexpected directory layout:') > -1) {
-			await execFile(goVersion.binaryPath, args, opts);
+			await execFile(goBinary, args, opts);
 		} else if (hasModSuffix(tool)) {
 			const gopath = env['GOPATH'];
 			if (!gopath) {
 				return `GOPATH not configured in environment`;
 			}
 			const destDir = gopath.split(path.delimiter)[0];
 			const outputFile = path.join(destDir, 'bin', process.platform === 'win32' ? `${tool.name}.exe` : tool.name);
-			await execFile(goVersion.binaryPath, ['build', '-o', outputFile, importPath], opts);
+			await execFile(goBinary, ['build', '-o', outputFile, importPath], opts);
 		}
 		const toolInstallPath = getBinPath(tool.name);
 		outputChannel.appendLine(`Installing ${toolImportPath} (${toolInstallPath}) SUCCEEDED`);