Move phpunit requirement from dev

Author: czukowski

README.md

@@ -16,7 +16,7 @@ Pick your version! Version numbering follows major PHPUnit version numbers, so f
 PHPUnit N.x, the installation command would look like this:
 
 ```sh
-composer require --dev czukowski/phpunit-sql "~N.0"
+composer require czukowski/phpunit-sql "~N.0"
 ```
 
 Usage

composer.json

@@ -15,10 +15,7 @@
         "issues": "https://github.com/czukowski/phpunit-sql/issues"
     },
     "require": {
-        "php": ">=7.0"
-    },
-    "require-dev": {
-        "phpunit/phpunit": "~6.0"
+        "phpunit/phpunit": "*"
     },
     "autoload": {
         "psr-4": {