Support PHPUnit 7, build with lowest and highest dependencies

Author: ondrejmirtes

.travis.yml

@@ -3,9 +3,13 @@ php:
   - 7.0
   - 7.1
   - 7.2
+env:
+  - dependencies=lowest
+  - dependencies=highest
 before_script:
   - composer self-update
-  - composer install
+  - if [ "$dependencies" = "lowest" ]; then composer update --prefer-lowest --no-interaction; fi;
+  - if [ "$dependencies" = "highest" ]; then composer update --no-interaction; fi;
 script:
   - vendor/bin/phing
 after_script:

composer.json

@@ -12,7 +12,7 @@
 	"require": {
 		"php": "~7.0",
 		"phpstan/phpstan": "^0.9.1",
-		"phpunit/phpunit": "^6.3"
+		"phpunit/phpunit": "^6.3 || ~7.0"
 	},
 	"require-dev": {
 		"consistence/coding-standard": "^2.0",