Close cache file properly

Fixes (reported by python 3.6):
Exception ignored in: <_io.FileIO name='/Users/michkapopoff/repo/pygccxml/unittests/data/new_cache.cache' mode='rb' closefd=True>
ResourceWarning: unclosed file <_io.BufferedReader name='/Users/michkapopoff/repo/pygccxml/unittests/data/new_cache.cache'>

Author: iMichka

pygccxml/parser/declarations_cache.py

@@ -220,14 +220,16 @@ def __load(file_name):
                                       % (file_name, len(list(cache.keys()))))
         except Exception as error:
             file_cache_t.logger.exception(
-                "Error occured while reading cache file: %s",
+                "Error occurred while reading cache file: %s",
                 error)
             cache_file_obj.close()
             file_cache_t.logger.info(
                 "Invalid cache file: [%s]  Regenerating." %
                 file_name)
             open(file_name, 'w+b').close()   # Create empty file
             cache = {}                       # Empty cache
+        finally:
+            cache_file_obj.close()
         return cache
 
     def flush(self):