function getFromEnv(env) {
  return definitions
    .filter((definition) => definition.hasOwnProperty('envVar'))
    .reduce((envMap, definition) => {
      const { key, envVar } = definition;
      if (env[envVar]) {
        envMap[key] = env[envVar];
      }
      return envMap;
    }, {});
}
Gets config values from environment
@param {object} env optional
@returns {object} configMap