Add defaultMeta to Logger index.d.ts (#1736)

* Update index.d.ts

* Update index.d.ts

Author: marikaner

index.d.ts

@@ -94,6 +94,7 @@ declare namespace winston {
     exceptions: ExceptionHandler;
     profilers: object;
     exitOnError: Function | boolean;
+    defaultMeta?: any;
 
     log: LogMethod;
     add(transport: Transport): Logger;