Lock development dependencies

Author: VasekPurchart

composer.json

@@ -12,10 +12,10 @@
 		"squizlabs/php_codesniffer": "^2.8.1"
 	},
 	"require-dev": {
-		"jakub-onderka/php-parallel-lint": "^0.9.2",
-		"phing/phing": "^2.16",
-		"phpstan/phpstan": "^0.6.3",
-		"phpunit/phpunit": "^6.0.1"
+		"jakub-onderka/php-parallel-lint": "0.9.2",
+		"phing/phing": "2.16",
+		"phpstan/phpstan": "0.6.4",
+		"phpunit/phpunit": "6.1.2"
 	},
 	"autoload": {
 		"psr-4": {