Install python3-dev when not using python2 (#551)

* Install python3-dev if use_python2==n

By default, ubuntu-based distros would install python2-dev if you
install python-dev.
python3-dev should be installed explicitly if we're not using python2.

* Add Emanuel Calso to contributors

CONTRIBUTORS.rst

@@ -69,6 +69,7 @@ Listed in alphabetical order.
   Davur Clementsen         `@dsclementsen`_              @davur
   Dónal Adams              `@epileptic-fish`_
   Dong Huynh               `@trungdong`_
+  Emanuel Calso            `@bloodpet`_                  @bloodpet
   Eraldo Energy            `@eraldo`_
   Eyad Al Sibai            `@eyadsibai`_
   Felipe Arruda            `@arruda`_
@@ -123,6 +124,7 @@ Listed in alphabetical order.
 .. _@andor-pierdelacabeza: https://github.com/andor-pierdelacabeza
 .. _@areski: https://github.com/areski
 .. _@arruda: https://github.com/arruda
+.. _@bloodpet: https://github.com/bloodpet
 .. _@bogdal: https://github.com/bogdal
 .. _@burhan: https://github.com/burhan
 .. _@c-rhodes: https://github.com/c-rhodes

{{cookiecutter.project_slug}}/utility/requirements.apt

@@ -3,7 +3,11 @@
 build-essential
 #required to translate
 gettext
+{% if cookiecutter.use_python2 == 'n' -%}
+python3-dev
+{% else %}
 python-dev
+{%- endif %}
 
 ##shared dependencies of:
 ##Pillow, pylibmc