Fix a text decoding issue

This was behaving differently between Python 2 and 3, causing
test 'test_dirty_work_dir' to fail in one of both.

bumpversion/vcs.py

@@ -67,7 +67,9 @@ def assert_nondirty(cls):
 
         if lines:
             raise WorkingDirectoryIsDirtyException(
-                "Git working directory is not clean:\n{}".format(b"\n".join(lines))
+                "Git working directory is not clean:\n{}".format(
+                    b"\n".join(lines).decode()
+                )
             )
 
     @classmethod
@@ -143,7 +145,7 @@ def assert_nondirty(cls):
         if lines:
             raise WorkingDirectoryIsDirtyException(
                 "Mercurial working directory is not clean:\n{}".format(
-                    b"\n".join(lines)
+                    b"\n".join(lines).decode()
                 )
             )
 

tests/test_cli.py

@@ -412,7 +412,7 @@ def test_dirty_work_dir(tmpdir, vcs):
 
     check_call([vcs, "add", "dirty"])
     vcs_name = "Mercurial" if vcs == "hg" else "Git"
-    vcs_output = "b'A dirty'" if vcs == "hg" else "b'A  dirty'"
+    vcs_output = "A dirty" if vcs == "hg" else "A  dirty"
 
     with pytest.raises(WorkingDirectoryIsDirtyException):
         with LogCapture() as log_capture: