Revert "Attempt to get travis to work by adding php-invoker"

This reverts commit 1396a958a5b96cc6c617ae725034fa58542acd25.
diff --git a/composer.json b/composer.json
index ec34372..54f305e 100644
--- a/composer.json
+++ b/composer.json
@@ -5,7 +5,6 @@
     },
     "require-dev": {
       "mikey179/vfsStream": "*",
-		  "phpunit/phpunit": "*",
-		  "phpunit/php-invoker": ">=1.1.0,<1.2.0"
+		  "phpunit/phpunit": "*"
 		}
 }
\ No newline at end of file