React-native: watchman--no-pretty get-sockname 返回，退出代码为空

我遵循 react native 页面的入门指南。 运行命令react-native run-ios我收到以下错误：

watchman--no-pretty get-sockname returned with exit code null dyld: Library not loaded: /usr/local/opt/pcre/lib/libpcre.1.dylib
  Referenced from: /usr/local/Cellar/watchman/4.5.0/libexec/bin/watchman
  Reason: image not found

 ERROR  watchman--no-pretty get-sockname returned with exit code null dyld: Library not loaded: /usr/local/opt/pcre/lib/libpcre.1.dylib
  Referenced from: /usr/local/Cellar/watchman/4.5.0/libexec/bin/watchman
  Reason: image not found

Error: watchman--no-pretty get-sockname returned with exit code null dyld: Library not loaded: /usr/local/opt/pcre/lib/libpcre.1.dylib
  Referenced from: /usr/local/Cellar/watchman/4.5.0/libexec/bin/watchman
  Reason: image not found

我的系统：macos 10.11.6，节点 6.2.2