Fix PHP version constraint

Author: Eugene Leonovich

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "tarantool/queue",
     "description": "PHP bindings for Tarantool Queue.",
-    "keywords": ["queue", "schedule", "delayed", "priority", "ttl", "ttr", "task", "job", "tarantool"],
+    "keywords": ["queue", "schedule", "delayed", "priority", "ttl", "ttr", "task", "job", "worker", "tarantool"],
     "type": "library",
     "license": "MIT",
     "authors": [
@@ -11,7 +11,7 @@
         }
     ],
     "require": {
-        "php": ">=5.4.0",
+        "php": "^5.4|^7.0",
         "ext-tarantool": "*"
     },
     "autoload": {