move fixtures package to require-dev section

Author: xabbuh

composer.json

@@ -14,10 +14,12 @@
     "require": {
         "php": ">=5.3.0",
         "guzzle/guzzle": "~3.7",
-        "php-xapi/exception": "~0.1",
-        "php-xapi/model": "~0.1",
-        "php-xapi/serializer": "~0.1",
-        "php-xapi/test-fixtures": "~0.1"
+        "php-xapi/exception": "^0.1.0",
+        "php-xapi/model": "^0.1.0",
+        "php-xapi/serializer": "^0.1.0"
+    },
+    "require-dev": {
+        "php-xapi/test-fixtures": "^0.1.0"
     },
     "autoload": {
         "psr-4": {