lowest dependency versions that pass tests

Author: ashnazg

composer.json

@@ -16,13 +16,13 @@
   },
   "require": {
     "php":              ">=7.1",
-    "league/flysystem": "~1.0.41"
+    "league/flysystem": ">=1.0.41"
   },
   "minimum-stability":  "stable",
   "require-dev": {
-    "mockery/mockery":  "~1.0",
-    "league/flysystem-memory": "~1.0",
-    "phpunit/phpunit": "^6.5"
+    "mockery/mockery":  "~1",
+    "league/flysystem-memory": "~1",
+    "phpunit/phpunit": "~6"
   },
   "extra": {
     "branch-alias": {