Use local version identifer for SHA

local version identifier seems to be the only PEP440
way to add arbitrary string to the version. Makes
pip stop complaining about invalid version label.

setup.py

@@ -32,7 +32,7 @@ if version.endswith(('a', 'b', 'rc')):
                              stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         out, err = p.communicate()
         if out:
-            version += '-' + out.decode('utf-8').strip()
+            version += '+' + out.decode('utf-8').strip()
     except Exception:
         pass