Support relative path for "path-to-lcov" argument

What

When I ran the following step after my test, the step failed

- name: Coveralls
      uses: coverallsapp/github-action@v1.1.2
      with:
        github-token: ${{ secrets.GITHUB_TOKEN }}
        path-to-lcov: ./my/path/relative.info

with the the error Lcov: file not found while if I specify with absolute path, it successes.

- name: Coveralls
      uses: coverallsapp/github-action@v1.1.2
      with:
        github-token: ${{ secrets.GITHUB_TOKEN }}
        path-to-lcov: ${{ github.workspace }}/path/relative/lcov.info

Start at the GitHub Action entry point that reads the path-to-lcov input and reproduce the failure using the relative-path example from the issue. Check how the action resolves that input versus an absolute path; done means relative .info paths are accepted while the existing absolute-path behavior remains working.