drop python 2.6 support

Author: mr-c

setup.py

@@ -24,7 +24,6 @@
       author_email='[email protected]',
       url="https://github.com/common-workflow-language/common-workflow-language",
       download_url="https://github.com/common-workflow-language/common-workflow-language",
-      extras_require={':python_version>="2.7"': ['typing']},
       license='Apache 2.0',
       packages=["cwltool"],
       package_data={'cwltool': ['schemas/draft-3/*.yml',
@@ -37,7 +36,8 @@
           'rdflib >= 4.1.0',
           'rdflib-jsonld >= 0.3.0',
           'shellescape',
-          'schema_salad == 1.7.20160316203940'
+          'schema_salad == 1.7.20160316203940',
+          'typing'
         ],
       test_suite='tests',
       tests_require=[],