Update _utils.py

Author: cclauss

Diff for: pyperf/_utils.py

@@ -193,7 +193,7 @@ def python_has_jit():
     implementation_name = python_implementation()
     if implementation_name == 'pypy':
         return sys.pypy_translation_info["translation.jit"]
-    elif implementation_name in ['graalpython', 'graalpy'] or (hasattr(sys, "pyston_version_info") or "pyston_lite" in sys.modules):
+    elif implementation_name in {'graalpython', 'graalpy'} or (hasattr(sys, "pyston_version_info") or "pyston_lite" in sys.modules):
         return True
     return False