Adding an environment variable before building your app

your-custom-build-script.sh

# 1. Add an enviroment variable on your bundle identifier on Xcode for example:
# com.yourAppName.$(PRODUCT_NAME:rfc1034identifier).${MY_ENV_VARIBLE}.
# 2. You should have a custom build script to execute on travis, so your .travis.yml look like this:
# ....
# script:
# - ./your-custom-build-script.sh
# ....
# 3. Set a value to this variable before your build with travis:

export MY_ENV_VARIBLE="customName"
xctool -workspace ${APP_NAME}.xcworkspace -scheme ${APP_NAME} # etc...

# Profit ! :)