Fixed compability with newer pip versions

setup.py

@@ -4,7 +4,7 @@
 # Copyright (c) 2015, Ayun Park. All rights reserved.
 # For licensing, see LICENSE file included in the package.
 import sys
-
+import pkgutil
 from setuptools import setup
 from setuptools.command.install import install
 
@@ -13,13 +13,8 @@ class NewInstall(install):
 
     @staticmethod
     def check_pymongo():
-        try:
-            from pip._internal import get_installed_distributions
-        except ImportError:
-            from pip import get_installed_distributions
-        for package in get_installed_distributions():
-            if package.project_name == 'pymongo':
-                return True
+        if pkgutil.find_loader('pymongo'):
+            return True
         return False
 
     def run(self):