Use context manager to avoid ResourceWarning

This implicitly will call close to avoid an unclosed file warning.

Author: leonardt

pyverilog/__init__.py

@@ -3,4 +3,5 @@
 
 import os
 
-__version__ = open(os.path.join(os.path.dirname(__file__), "VERSION")).read().splitlines()[0]
+with open(os.path.join(os.path.dirname(__file__), "VERSION")) as f:
+    __version__ = f.read().splitlines()[0]