Add gateway map to rotation (#301)

Changes made via GitHub editor. I'll test as soon as I get home ~2.5-3
hours from now.

resources/maps/GatewayToTheAtlantic.json

@@ -1,7 +1,7 @@
 {
-  "name": "Britannia",
-  "width": 2000,
-  "height": 1397,
+  "name": "GatewayToTheAtlantic",
+  "width": 2216,
+  "height": 1968,
   "nations": [
     {
       "coordinates": [2144, 344],

src/server/Master.ts

@@ -285,6 +285,7 @@ function getNextMap(): GameMapType {
     Asia: 2,
     Mars: 2,
     Britannia: 2,
+    GatewayToTheAtlantic: 2,
   };
 
   Object.keys(GameMapType).forEach((key) => {