Bumped to 2.3.1 to fix pypi

Summary: Can't modify autobid for 2.3.0 on pypi so bumping version

Test Plan: Reading diff

Author: Evan Chen

facebookads/api.py

@@ -129,7 +129,7 @@ class FacebookAdsApi(object):
             this sdk.
     """
 
-    SDK_VERSION = '2.3.0'
+    SDK_VERSION = '2.3.1'
 
     API_VERSION = 'v2.3'
 

setup.py

@@ -29,7 +29,7 @@
 requirements_filename = os.path.join(this_dir, 'requirements.txt')
 
 PACKAGE_NAME = 'facebookads'
-PACKAGE_VERSION = '2.3.0'
+PACKAGE_VERSION = '2.3.1'
 PACKAGE_AUTHOR = 'Facebook'
 PACKAGE_AUTHOR_EMAIL = ''
 PACKAGE_URL = 'https://github.com/facebook/facebook-python-ads-sdk'