title: Uncaught TypeError: Object(...) is not a function for Cordova plugin reference
body: <p>I created a cordova plugin using plugman and am trying to use it in my ionic app. But I am getting Uncaught TypeError: Object(...) is not a function... I am unable to figure out what this error is.</p>
  
  <p>Did some research and found that upgrading ionic-native version might work but it did not in my case.</p>
  
  <p>I am trying to create a wrapper service for the plugin like this:</p>
  
  <pre><code>    import { Injectable } from '@angular/core';
      import { Plugin, Cordova, IonicNativePlugin } from '@ionic-native/core';
  
      @Plugin({
        pluginName: 'mathcalculator',
        plugin: 'cordova.plugin.mathcalculator',
        pluginRef: 'MathCalculator', 
        repo: 'https://github.com/dkandel/MathCalculator.git', 
        platforms: ['Android']
      })
  
      @Injectable({
       providedIn: 'root'
      })
      export class MathService extends IonicNativePlugin {
  
        @Cordova()
        add(args: any): Promise&lt;any&gt; {
         return;
        }
      }
  </code></pre>
  
  <p>The service has been added to the providers in App module file. 
  I also have the plugin in my plugins folder. When i try to run the app I keep getting Object(...) is not a function and the error points to @Cordova() on my service file. </p>
  
  <p>Can anyone help me out please?</p>