Fixed the code sample code for ngFor

[aartisharma22]

The text that appears on https://valor-software.com/ng2-dragula/index.html in ngFor example is incorrect and doesn't work if copied as is. So this modification to fix it so anybody can copy it directly from demo site.

Please briefly describe your changes, and explain any choices you made.

Relevant issues

Please include references to any relevant issues.

Before submitting

If your pull request includes changes to the library code:

• [ ] Add tests (in modules/ng2-dragula/src/spec/...) for any code you have changed
• [ ] Make sure the test suite passes
• [ ] Make sure the demo app isn't broken

[codecov[bot]]

Codecov Report

Merging #956 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #956   +/-   ##
=====================================
  Coverage      84%    84%           
=====================================
  Files           8      8           
  Lines         300    300           
  Branches       38     38           
=====================================
  Hits          252    252           
  Misses         31     31           
  Partials       17     17

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