fix bug when using callable version_scheme

This fixes bug introduced with 0f1c98d,
looking like this:

    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-zfpnaarq/xd-docker/setup.py", line 69, in <module>
        setup_requires=['setuptools_scm'],
      File "/usr/local/lib/python3.4/distutils/core.py", line 108, in setup
        _setup_distribution = dist = klass(attrs)
      File "/usr/local/lib/python3.4/site-packages/setuptools/dist.py", line 272, in __init__
        _Distribution.__init__(self,attrs)
      File "/usr/local/lib/python3.4/distutils/dist.py", line 280, in __init__
        self.finalize_options()
      File "/usr/local/lib/python3.4/site-packages/setuptools/dist.py", line 327, in finalize_options
        ep.load()(self, ep.name, value)
      File "/usr/local/lib/python3.4/site-packages/setuptools_scm-1.10.2.dev8+ng4835e4d-py3.4.egg/setuptools_scm/integration.py", line 16, in version_keyword
    AttributeError: 'function' object has no attribute 'pop'

Signed-off-by: Esben Haabendal <[email protected]>

Author: esben

setuptools_scm/integration.py

@@ -12,10 +12,10 @@ def version_keyword(dist, keyword, value):
         return
     if value is True:
         value = {}
-    if os.path.exists('PKG-INFO'):
-        value.pop('root', None)
     if getattr(value, '__call__', None):
         value = value()
+    if os.path.exists('PKG-INFO'):
+        value.pop('root', None)
     dist.metadata.version = get_version(**value)