React-native: watchman--no-pretty get-sockname renvoyé avec le code de sortie null

Je suis le guide de démarrage de la page de réaction native. Après avoir exécuté la commande react-native run-ios j'ai eu l'erreur suivante :

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

mon système : macos 10.11.6, nœud 6.2.2