title: ng2-dragula in angular7 failed to compile
body: <p>Using a default startup Angular-Cli 7 project and following the steps as described here: <a href="https://github.com/valor-software/ng2-dragula" rel="nofollow noreferrer">https://github.com/valor-software/ng2-dragula</a> to setup ng2-dragula, failed to compile.</p>
  
  <p>ng2-dragula 2.1.0 (latest).</p>
  
  <p>Details message:</p>
  
  <pre><code>ERROR in node_modules/ng2-dragula/dist/MockDrake.d.ts(41,5): error      TS2416:    Property 'on' in type 'MockDrake' is not assignable to the same property in base type 'DrakeWithModels'.
  Type '(event: string, callback: Function) =&gt; void' is not assignable to type '(events: string, callback: Function) =&gt; Drake'.
  Type 'void' is not assignable to type 'Drake'.
  
  i ｢wdm｣: Failed to compile.
  </code></pre>
  
  <p>Dev. System Info:</p>
  
  <pre><code>Angular CLI: 7.0.3
  Node: 8.11.4
  OS: win32 x64
  Angular: 7.0.1
  ... animations, common, compiler, compiler-cli, core, forms
  ... http, language-service, platform-browser
  ... platform-browser-dynamic, router
  
  Package                           Version
  -----------------------------------------------------------
  @angular-devkit/architect         0.10.3
  @angular-devkit/build-angular     0.10.3
  @angular-devkit/build-optimizer   0.10.3
  @angular-devkit/build-webpack     0.10.3
  @angular-devkit/core              7.0.3
  @angular-devkit/schematics        7.0.3
  @angular/cli                      7.0.3
  @ngtools/webpack                  7.0.3
  @schematics/angular               7.0.3
  @schematics/update                0.10.3
  rxjs                              6.3.3
  typescript                        3.1.3
  webpack                           4.19.1
  </code></pre>