[cesium] update linting config

types/cesium/index.d.ts

@@ -6,6 +6,7 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
+// tslint:disable-next-line:export-just-namespace
 export = Cesium;
 export as namespace Cesium;
 

types/cesium/tslint.json

@@ -1 +1,6 @@
-{ "extends": "dtslint/dt.json" }
+{
+    "extends": "dtslint/dt.json",
+    "rules": {
+        "strict-export-declare-modifiers": false
+    }
+}