Fix an error when trying to move the lock file on Python 2.7

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed an error when installing from private repositories.
+- Fixed an error when trying to move the lock file on Python 2.7.
 
 
 ## [0.12.1] - 2018-10-17

poetry/poetry.py

@@ -188,7 +188,7 @@ class Poetry:
             # Checking for pyproject.lock
             old_lock = poetry_file.with_suffix(".lock")
             if old_lock.exists():
-                shutil.move(old_lock, lock)
+                shutil.move(str(old_lock), str(lock))
 
         locker = Locker(poetry_file.parent / "poetry.lock", local_config)