Add phpstan to travis

.travis.yml

@@ -1,26 +1,39 @@
 language: php
 sudo: required
 php:
-  - 5.5
-  - 5.6
-  - 7.0
-  - 7.1
-  - 7.2
-  - 7.3
+- 5.5
+- 5.6
+- 7.0
+- 7.1
+- 7.2
+- 7.3
+
+env:
+  global:
+  - RUN_PHPSTAN="FALSE"
+
+matrix:
+  include:
+  - name: 'PHPStan'
+    php: 7.2
+    env: RUN_PHPSTAN="TRUE"
+  fast_finish: true
+  allow_failures:
+  - php: 5.5
+
+install:
+- if [ $RUN_PHPSTAN == "TRUE"  ]; then wget https://github.com/phpstan/phpstan/releases/download/0.10.3/phpstan.phar; fi
 
 before_script:
 - composer install
 
 script:
-  - ./bin/phpunit --configuration tests/phpunit.xml --coverage-clover=coverage.xml
+- if [ $RUN_PHPSTAN == "FALSE"  ]; then ./bin/phpunit --configuration tests/phpunit.xml --coverage-clover=coverage.xml; fi
+- if [ $RUN_PHPSTAN == "TRUE"  ]; then php phpstan.phar analyse -c phpstan.neon lib; fi
 
 after_success:
 - bash <(curl -s https://codecov.io/bash)
 
 cache:
   directories:
-    - $HOME/.composer/cache
-
-matrix:
-  allow_failures:
-    - php: 5.5
+  - $HOME/.composer/cache

phpstan.neon

@@ -0,0 +1,3 @@
+parameters:
+  level: 0
+  bootstrap: %currentWorkingDirectory%/vendor/autoload.php