Add support for HTTP{S}_PROXY env variables (#162)

matterclient/matterclient.go

@@ -106,7 +106,7 @@ func (m *MMClient) Login() error {
 	}
 	// login to mattermost
 	m.Client = model.NewClient(uriScheme + m.Credentials.Server)
-	m.Client.HttpClient.Transport = &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: m.SkipTLSVerify}}
+	m.Client.HttpClient.Transport = &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: m.SkipTLSVerify}, Proxy: http.ProxyFromEnvironment}
 	m.Client.HttpClient.Timeout = time.Second * 10
 
 	for {