Change property visibility.

src/operations/category.ts

@@ -1,7 +1,8 @@
 // vim: set tw=80 ts=2 sw=2 sts=2 :
 
 export class Category {
-  category: string;
-  expenses: number;
-  revenues: number;
+  public category: string;
+  public expenses: number;
+  public revenues: number;
+  public income: number;
 }