setup.py: Move 'nose' to tests_require

Moves 'nose' from ``install_requires`` field to
``tests_require`` field of config object as 'nose'
is not required for installation of the package
but only for running the tests.

Fixes https://gitlab.com/balasankarc/gemfileparser/issues/1

Author: satwikkansal

setup.py

@@ -82,7 +82,8 @@
 
 .. _GNU GPL version 3 (or above) License: http://www.gnu.org/licenses/gpl
 ''',
-    'install_requires': ['nose'],
+    'install_requires': [],
+    'tests_require': ['nose'],
     'packages': ['gemfileparser'],
     'scripts': [],
     'name': 'gemfileparser'