Fix the default task so that clean is run first
Fix the default task so that clean is run first

Make clean a dependency and then execute build with gulp.start to avoid
running them concurrently.

unicef/rhizome,unicef/polio,unicef/rhizome,unicef/polio,unicef/rhizome,unicef/rhizome,unicef/polio,SeedScientific/polio,SeedScientific/polio,SeedScientific/polio,unicef/polio,SeedScientific/polio,SeedScientific/polio