Increase Psalm error level

Author: scheb

.travis.yml

@@ -52,7 +52,7 @@ jobs:
     - name: Psalm
       php: 7.4
       script:
-        - ./bin/psalm --show-info=true
+        - ./bin/psalm
 
     - name: PHP Code Style Sniffer
       php: 7.4

CONTRIBUTING.md

@@ -32,5 +32,5 @@ Before you create a pull request, please make sure your changes fulfill the qual
 1) Install the dependencies with `composer install`
 2) Run the PHPUnit tests with `bin/phpunit`
 3) Run PHP CodeSniffer with `bin/phpcs --standard=php_cs.xml --ignore=/vendor/ .`
-4) Run Psalm with `bin/psalm`
-5) Ideally, run [PHP-CS-Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) (not provided with the library)
+4) Run Psalm with `bin/psalm` and address any error-level issues
+5) Run [PHP-CS-Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) (not provided with the library)

psalm.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <psalm
     resolveFromConfigFile="true"
-	errorLevel="3"
+	errorLevel="2"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"