Hard-coded runner directory

[dlakatos847]

Github Actions workspace path value can be anything theoretically. For example, act sets the GITHUB_WORKSPACE variable a custom value.

markdown-to-pdf/src/github_interface.js

Line 12 in 1be2677

const RUNNER_DIR = '/github/workspace/';

Unfortunately, the referenced variable is hard-coded preventing the use of custom GITHUB_WORKSPACE variable value. RUNNER_DIR should read the workspace path from the environment variables instead.