Fixed phpstan in CI build

Author: thomasvargiu

.travis.yml

@@ -31,7 +31,6 @@ matrix:
       env:
         - DEPS=locked
         - LEGACY_DEPS="ocramius/proxy-manager phpbench/phpbench phpunit/phpunit"
-        - PHPSTAN_TEST=true
     - php: 7
       env:
         - DEPS=latest
@@ -44,6 +43,7 @@ matrix:
         - BENCHMARKS=true
         - CS_CHECK=true
         - TEST_COVERAGE=true
+        - PHPSTAN_TEST=true
     - php: 7.1
       env:
         - DEPS=latest