Update __init__.py

Use context manager for file opening.

Author: sp1rs

wiremock/__init__.py

@@ -1,4 +1,5 @@
 import os
 
 __wiremock_version_path__ = os.path.realpath(__file__ + '/../VERSION')
-__version__ = open(__wiremock_version_path__, 'r').readline().strip()
+with open(__wiremock_version_path__, 'r') as f:
+    __version__ = f.readline().strip()