dependencies: upgrade graceful-fs 4.1.15 -> 4.2.2
dependencies: upgrade graceful-fs 4.1.15 -> 4.2.2

Without this, on nodejs 10 and 12 (and maybe 8, not tested), Etherpad failed to
start, throwing the following error:

  [2019-10-22 19:01:01.439] [ERROR] console - exception thrown: Maximum call stack size exceeded
  [2019-10-22 19:01:01.439] [INFO] console - RangeError: Maximum call stack size exceeded
      at Function.[Symbol.hasInstance] (<anonymous>)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:194:14)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)
      at ReadStream (/opt/etherpad-lite/src/node_modules/graceful-fs/graceful-fs.js:195:28)

Fixes #3654.

storytouch/etherpad-lite,aptivate/etherpad-lite,aptivate/etherpad-lite,aptivate/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,aptivate/etherpad-lite,joequant/etherpad-lite,joequant/etherpad-lite,storytouch/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,ether/etherpad-lite