function setCacheValueSync (cachePath, key, value) {
  var originalCache;
  try {
    originalCache = readCacheSync(cachePath);
  } catch (e) {
    originalCache = {};
  }
  var newCache = _.assign(originalCache, {
    [key]: value
  });
  fs.writeFileSync(cachePath, JSON.stringify(newCache, null, '  '));
  return newCache;
}
Sets a cache value and writes the file to disk