Add support for reading http.proxy setting (#639)

* Add support for reading http.proxy setting

* fix proxy config

1. set both lower and upper case proxy environment variable
2. do not touch process.env when http.proxy setting is not present

src/goInstallTools.ts

@@ -115,9 +115,20 @@ function installTools(goVersion: SemVersion, missing?: string[]) {
 
 	outputChannel.appendLine(''); // Blank line for spacing.
 
+	// http.proxy setting takes precedence over environment variables
+	let httpProxy = vscode.workspace.getConfiguration('http').get('proxy');
+	let env = process.env;
+	if (httpProxy) {
+		env = Object.assign({}, process.env, {
+			http_proxy: httpProxy,
+			HTTP_PROXY: httpProxy,
+			https_proxy: httpProxy,
+			HTTPS_PROXY: httpProxy,
+		});
+	}
 	missing.reduce((res: Promise<string[]>, tool: string) => {
 		return res.then(sofar => new Promise<string[]>((resolve, reject) => {
-			cp.execFile(goRuntimePath, ['get', '-u', '-v', tools[tool]], { env: process.env }, (err, stdout, stderr) => {
+			cp.execFile(goRuntimePath, ['get', '-u', '-v', tools[tool]], { env }, (err, stdout, stderr) => {
 				if (err) {
 					outputChannel.appendLine('Installing ' + tool + ' FAILED');
 					let failureReason = tool + ';;' + err + stdout.toString() + stderr.toString();