update dependenis and fix flake8 error

requirements/production.txt

@@ -11,7 +11,7 @@ diff-match-patch==20121119  # via django-import-export
 django-import-export==1.0.0
 django-social-authsch==0.1
 django-solo==1.1.3
-django==2.0.1
+django>=2.0.10
 djangorestframework==3.7.7
 et-xmlfile==1.0.1         # via openpyxl
 gunicorn==19.7.1
@@ -23,14 +23,14 @@ openpyxl==2.5.0           # via tablib
 pyjwt==1.5.3              # via social-auth-core
 python3-openid==3.1.0     # via social-auth-core
 pytz==2017.3              # via django
-pyyaml==3.12              # via tablib
+pyyaml>=4.2b1              # via tablib
 requests-oauthlib==0.8.0  # via social-auth-core
-requests==2.18.4          # via requests-oauthlib, social-auth-core
+requests>=2.20.0         # via requests-oauthlib, social-auth-core
 six==1.11.0               # via social-auth-app-django, social-auth-core
 social-auth-app-django==2.1.0  # via django-social-authsch
 social-auth-core==1.6.0   # via django-social-authsch, social-auth-app-django
 tablib==0.12.1            # via django-import-export
 unicodecsv==0.14.1        # via tablib
-urllib3==1.22             # via requests
+urllib3>=1.23             # via requests
 xlrd==1.1.0               # via tablib
 xlwt==1.3.0               # via tablib