[travis] improve coveralls and cache

.travis.yml

@@ -5,6 +5,7 @@ language: php
 cache:
   directories:
     - $HOME/.composer/cache
+    - vendor
 
 matrix:
   fast_finish: true
@@ -22,8 +23,6 @@ matrix:
 
 before_install:
   - if [[ $EXECUTE_TEST_COVERALLS != 'true' ]]; then phpenv config-rm xdebug.ini || return 0; fi
-  - composer self-update
-  - if [[ $EXECUTE_TEST_COVERALLS == 'true' ]]; then composer require --dev --no-update satooshi/php-coveralls; fi
 
 install:
   - travis_retry composer update --no-interaction $COMPOSER_ARGUMENTS
@@ -35,4 +34,8 @@ script:
   - if [[ $EXECUTE_CS_CHECK == 'true' ]]; then ./vendor/bin/php-cs-fixer fix -v --diff --dry-run; fi
 
 after_script:
-  - if [[ $EXECUTE_TEST_COVERALLS == 'true' ]]; then travis_retry ./vendor/bin/coveralls -v; fi
+  - if [[ $EXECUTE_TEST_COVERALLS == 'true' ]]; then
+    wget https://github.com/satooshi/php-coveralls/releases/download/v1.0.1/coveralls.phar;
+    chmod +x coveralls.phar;
+    php coveralls.phar -v;
+    fi