Use shared StartupError class

Remove separate StartupError class definition in master.js in favor of
the shared StartupError class in lib/error.js.

master.js

@@ -542,9 +542,6 @@ async function getPlugins(){
 	return plugins;
 }
 
-// Errror class for known errors occuring during startup
-class StartupError extends Error { }
-
 /**
  * Calls listen on server capturing any errors that occurs
  * binding to the port.
@@ -552,7 +549,7 @@ class StartupError extends Error { }
 function listen(server, ...args) {
 	return new Promise((resolve, reject) => {
 		function wrapError(err) {
-			reject(new StartupError(
+			reject(new errors.StartupError(
 				`Server listening failed: ${err.message}`
 			));
 		}
@@ -640,7 +637,7 @@ async function startServer() {
 			privateKey = await fs.readFile(config.sslPrivKey);
 
 		} catch (err) {
-			throw new StartupError(
+			throw new errors.StartupError(
 				`Error loading ssl certificate: ${err.message}`
 			);
 		}
@@ -680,19 +677,19 @@ I           version of clusterio.  Expect things to break. I
 `
 	);
 	startServer().catch(err => {
-		if (!(err instanceof StartupError)) {
+		if (err instanceof errors.StartupError) {
+			console.error(`
++----------------------------------+
+| Unable to to start master server |
++----------------------------------+`
+			);
+		} else {
 			console.error(`
 +---------------------------------------------------------------+
 | Unexpected error occured while starting master, please report |
 | it to https://github.com/clusterio/factorioClusterio/issues   |
 +---------------------------------------------------------------+`
 			);
-		} else {
-			console.error(`
-+----------------------------------+
-| Unable to to start master server |
-+----------------------------------+`
-			);
 		}
 
 		console.error(err);