title: error TS2339: Property 'combineLatest' does not exist on type 'typeof Observable'
body: <p>I have a problem when I try to start my angular 6 project. I've got this error : </p>
  
  <p>"TSError: ⨯ Unable to compile TypeScript:
  git.version.ts(34,29): error TS2339: Property 'combineLatest' does not exist on type 'typeof Observable'."</p>
  
  <p>It worked well with Angular 5 but I updated RxJs (from 5 to 6) and now it doesn't work. </p>
  
  <pre class="lang-js prettyprint-override"><code>import { readFileSync, writeFileSync } from 'fs';
  import { join } from 'path';
  import { Observable, combineLatest } from 'rxjs';
  
  
  let exec = require('child_process').exec;
  
  let tag = new Observable&lt;string&gt;(s =&gt; {
      exec('git describe --tags $(git rev-list --tags --max-count=1)',
          function (error: Error, stdout: Buffer, stderr: Buffer) {
              if (error !== null) {
                  console.log('git error: ' + error + stderr);
              }
              s.next(stdout.toString().trim());
              s.complete();
          });
  });
  
  
  
  let revision = new Observable&lt;string&gt;(s =&gt; {
      exec('git rev-parse --short HEAD',
          function (error: Error, stdout: Buffer, stderr: Buffer) {
              if (error !== null) {
                  console.log('git error: ' + error + stderr);
              }
              s.next(stdout.toString().trim());
              s.complete();
          });
  });
  
  Observable.combineLatest(tag, revision).subscribe(([tag, revision]) =&gt; {
          console.log(`version: '${tag}', revision: '${revision}'`);
  
          const content = '// this file is automatically generated\n' +
              `export const version = {version: '${tag}', revision: '${revision}'};`;
  
          writeFileSync(
              'src/environments/version.ts',
              content,
              {encoding: 'utf8'}
          );
      });
  </code></pre>
  
  <p>The command I launch : "ts-node git.version.ts" is to get the commit and the tag version I work with.</p>
  
  <p>Thank you very much !</p>
  
  <p>UPDATE : </p>
  
  <pre><code>combineLatest(tag, revision).subscribe(([tag, revision]) =&gt; {
          console.log(`version: '${tag}', revision: '${revision}'`);
  
          const content = '// this file is automatically generated\n' +
              `export const version = {version: '${tag}', revision: '${revision}'};`;
  
          writeFileSync(
              'src/environments/version.ts',
              content,
              {encoding: 'utf8'}
          );
      });
  </code></pre>
  
  <p>I haven't any error about CombineLatest but I have an error from ts-node : </p>
  
  <pre><code>function (exports, require, module, __filename, __dirname) { import { writeFileSync } from 'fs';
                                                                ^^^^^^
  
  SyntaxError: Unexpected token import
  </code></pre>
  
  <p>Any idea ?</p>
  
  <p>UPDATE 2 : To fix this error : </p>
  
  <pre><code>"config": "ts-node -O '{\"module\": \"commonjs\"}' git.version.ts",
  </code></pre>
  
  <p>In package.json</p>