My Ionic info:
cli packages: (/usr/lib/node_modules) @ionic/cli-utils : 1.9.2 ionic (Ionic CLI) : 3.9.2 global packages: Cordova CLI : 7.0.1 local pack
When I use ionic cli build app(ionic3 + angular5),same problem happened to me.I updated '@ionic/app-scripts' to version '3.1.6',then problem solved