Firebase Stub: added support for data remove

__mocks__/gatsby-plugin-firebase/constants/database.js

@@ -1,6 +1,7 @@
 import AuthConstants from './auth';
 
 const valueEventType = 'value';
+const childRemovedEventType = 'child_removed';
 
 const resumesPath = 'resumes';
 const usersPath = 'users';
@@ -24,6 +25,10 @@ class Database {
     return valueEventType;
   }
 
+  static get childRemovedEventType() {
+    return childRemovedEventType;
+  }
+
   static get resumesPath() {
     return resumesPath;
   }