title: @angular/common/http has no exported member 'RequestOptions'
body: <p>I want to sand emails with angular 6 using an firebase function, but angular throws this error:</p>
  <blockquote>
  <p>error TS2305: Module '&quot;E:/project/node_modules/@angular/common/http&quot;'
  has no exported member 'RequestOptions'.</p>
  </blockquote>
  <pre class="lang-js prettyprint-override"><code>import { Injectable } from '@angular/core';
  import { NgForm } from '@angular/forms';
  import { HttpClient, HttpHeaders, RequestOptions } from '@angular/common/http';
  import 'rxjs';
  @Injectable()
  export class MailerService {
      constructor(private httpClient: HttpClient) { }
      send(form: NgForm) {
          let url = 'TheUrlOfMyFunction';
          let params: URLSearchParams = new URLSearchParams();
          let options = {headers: new HttpHeaders({'Content-Type':  'application/json'})};
          params.set('to', form.value['emailTo']);
          params.set('from', form.value['emailFrom']);
          params.set('subject', form.value['object']);
          params.set('content', form.value['text']);
          return this.httpClient.post(url, params, options)
                          .toPromise()
                          .then( res =&gt; { console.log(res) })
                          .catch(err =&gt; { console.log(err) })
      }
  }
  </code></pre>