[fix] drop Python 2: use importlib instead of imp.load_source

imp.load_source is not documented in Python 3
see documentation : https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly

partial fix of https://github.com/searx/searx/issues/1674

searx/utils.py

@@ -3,8 +3,8 @@ import os
 import sys
 import re
 import json
+import importlib
 
-from imp import load_source
 from numbers import Number
 from os.path import splitext, join
 from io import open
@@ -445,8 +445,11 @@ def load_module(filename, module_dir):
     if modname in sys.modules:
         del sys.modules[modname]
     filepath = join(module_dir, filename)
-    module = load_source(modname, filepath)
-    module.name = modname
+    # and https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
+    spec = importlib.util.spec_from_file_location(modname, filepath)
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[modname] = module
+    spec.loader.exec_module(module)
     return module