DJANGO_SENTRY_DSN env variable if use_sentry

Closes pydanny/cookiecutter-django#446

CONTRIBUTORS.rst

@@ -64,6 +64,7 @@ Listed in alphabetical order
   Cristian Vargas          `@cdvv7788`_
   Cullen Rhodes            `@c-rhodes`_
   Daniele Tricoli          `@eriol`_
+  Davur Clementsen         `@dsclementsen`_             @davur
   Eyad Al Sibai            `@eyadsibai`_
   Felipe Arruda            `@arruda`_
   Garry Cairns             `@garry-cairns`_

{{cookiecutter.repo_name}}/env.example

@@ -12,7 +12,7 @@ DJANGO_MAILGUN_API_KEY=
 DJANGO_MAILGUN_SERVER_NAME=
 DJANGO_SERVER_EMAIL=
 DJANGO_SECURE_SSL_REDIRECT=False
-{% if cookiecutter.use_whitenoise == 'y' -%}
+{% if cookiecutter.use_sentry == 'y' -%}
 DJANGO_SENTRY_DSN=
 {% endif %}
 {% if cookiecutter.use_newrelic == 'y' -%}