setup: Install some deps on Py2.7 only

Lockfile and dict.sorted are only used in pungi.gather module, which
does not work with Python 3 due to dependency on yum. There's no point
in always pulling in these two libraries there.

This change fixes issues with python dependencies generator that puts
python3.6dist(lockfile) into RPM requires.

For builds on Python 2.6 these libraries are actually needed, but there
are no generators on RHEL 6. So this change can only break development
on RHEL 6. And if someone needs to do that, they have bigger problems...

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

setup.py

@@ -60,16 +60,16 @@ setup(
     install_requires = [
         "jsonschema",
         "kobo",
-        "lockfile",
         "lxml",
         "productmd",
         "six",
         'dogpile.cache',
-        'dict.sorted',
         ],
     extras_require={
         ':python_version=="2.7"': [
             'enum34'
+            "lockfile",
+            'dict.sorted',
         ]
     },
     tests_require = [