fixed monitor map image overflow width when screen is large

src/routes/Dashboard/Monitor.less

@@ -4,9 +4,11 @@
 .mapChart {
   padding-top: 24px;
   height: 457px;
+  text-align: center;
   img {
-    width: 100%;
-    max-height: 457px;
+    display: inline-block;
+    max-width: 100%;
+    max-height: 437px;
   }
 }