Returns the response body string for a Github path

Property definitions

github $ MockGithubAPI :: response_string
	# Returns the response body string for a Github `path`
	fun response_string(path: String): String do
		var file = response_file(path)
		assert file.file_exists
		return file.to_path.read_all
	end
lib/github/tests/test_api.nit:104,2--109,4