Fix UnicodeDecodeError on venv error

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed handling of `in` environment markers with commas.
+- Fixed a `UnicodeDecodeError` when an error occurs in venv.
 
 
 ## [0.10.1] - 2018-05-28

poetry/utils/venv.py

@@ -23,7 +23,7 @@ class VenvCommandError(VenvError):
 
     def __init__(self, e):  # type: (CalledProcessError) -> None
         message = 'Command {} errored with the following output: \n{}'.format(
-            e.cmd, e.output.decode()
+            e.cmd, decode(e.output)
         )
 
         super(VenvCommandError, self).__init__(message)