Be a little more explicit on the types

Author: Bryan Mikaelian

lib/index.d.ts

@@ -5,7 +5,13 @@ export declare namespace SegmentAnalytics {
     context?: object;
   }
 
-  interface IntegrationsSettings {
+  type IntegrationSettings = BaseIntegrationSettings | SegmentIOIntegrationSettings
+
+  interface BaseIntegrationSettings {
+    [key: string]: unknown
+  }
+
+  interface SegmentIOIntegrationSettings {
     addBundledMetadata: boolean;
     apiHost?: string;
     apiKey?: string;