CI - fix installing phpstan (BC in 0.10)

Don't need latest version for Travis.
BC in 0.10 (https://github.com/phpstan/phpstan/releases/tag/0.10)
https://travis-ci.org/EdgedesignCZ/phpqa/jobs/397310631#L770

bin/suggested-tools.sh

@@ -16,7 +16,7 @@ then
         composer require symfony/filesystem:~2 symfony/process:~2 symfony/finder:~2 jakub-onderka/php-parallel-lint jakub-onderka/php-console-highlighter phpstan/phpstan:~0.8.0 friendsofphp/php-cs-fixer:~2.2 vimeo/psalm:~1 sensiolabs/security-checker $requireMode
     else
         # symfony 3
-        composer require jakub-onderka/php-parallel-lint jakub-onderka/php-console-highlighter phpstan/phpstan friendsofphp/php-cs-fixer:~2.2 vimeo/psalm:~1 sensiolabs/security-checker
+        composer require jakub-onderka/php-parallel-lint jakub-onderka/php-console-highlighter phpstan/phpstan:~0.9.0 friendsofphp/php-cs-fixer:~2.2 vimeo/psalm:~1 sensiolabs/security-checker
     fi
 else
     echo "Removing suggested tools"