Modify behavior of options set to false

I'm using [generator-latex](https://github.com/LeoColomb/generator-latex) that is a yeoman generator for LaTeX project.
However, bibtex support of generator-latex doesn't run correctly.
Task configuration is as follows:
```
  grunt.initConfig({
    latex: {
      pdf: {
        src: 'main.tex',
        options: {
          outputDirectory: 'dist/',
          jobname: 'document'
        }
      },
      bib: {
        src: 'dist/document.aux',
        options: {
          engine: 'bibtex',
          interaction: false
        }
      }
    }
```
And, console output is as follows:
```
Running "latex:bib" (latex) task
[ 'bibtex', '', 'document.aux' ]
bibtex: Need exactly one file argument.
Try `bibtex --help' for more information.
```

In this case, `interaction` option must be ignored and console output must be `[ 'bibtex', 'document.aux' ]`.
I modified extractOptions to ignore options set to false.