Run PHPStan on travis only once

When running it on PHP 7.2 it runs twice, because the lowest dependencies check is run on this version, too.

.travis.yml

@@ -34,7 +34,7 @@ before_script:
 script:
   - if [[ $(phpenv version-name) == '7.2' ]]; then vendor/bin/phpunit --coverage-clover clover.xml ; fi
   - if [[ $(phpenv version-name) != '7.2' ]]; then vendor/bin/phpunit ; fi
-  - if [[ $(phpenv version-name) == '7.2' ]]; then vendor/bin/phpstan analyse -l 5 -c phpstan.neon src ; fi
+  - if [[ $(phpenv version-name) == '7.3' ]]; then vendor/bin/phpstan analyse -l 5 -c phpstan.neon src ; fi
 
 after_script:
   - if [[ $(phpenv version-name) == '7.2' ]]; then php vendor/bin/coveralls -v ; fi