Install coveralls only when we are about to use it

coveralls installs guzzlehttp/guzzle, which is a version 6 guzzle
client, and incompatible with v4/v5... causing tests to error!

Author: weierophinney

.travis.yml

@@ -66,14 +66,14 @@ install:
   - if [[ $LEGACY_DEPS != '' ]]; then travis_retry composer update $COMPOSER_ARGS --with-dependencies $LEGACY_DEPS ; fi
   - if [[ $DEPS == 'latest' ]]; then travis_retry composer update $COMPOSER_ARGS ; fi
   - if [[ $DEPS == 'lowest' ]]; then travis_retry composer update --prefer-lowest --prefer-stable $COMPOSER_ARGS ; fi
-  - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry composer require --dev $COMPOSER_ARGS $COVERAGE_DEPS ; fi
   - stty cols 120 && composer show
 
 script:
   - if [[ $TEST_COVERAGE == 'true' ]]; then composer run-script test-coverage -- --verbose ; else composer run-script test -- --verbose ; fi
   - if [[ $CS_CHECK == 'true' ]]; then composer cs-check ; fi
 
 after_script:
+  - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry composer require --dev $COMPOSER_ARGS $COVERAGE_DEPS ; fi
   - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry vendor/bin/php-coveralls -v ; fi
 
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