remove escape character from pexpect.spawn.interact

The default escape character for pexpect.spaw is ctrl-]
which conflicts with a vim binding. This isn't an escape
sequence that is mirrored in virtualenv, so there doesn't
seem to be a good reason to keep it. This will make `pipenv
shell` more inline with the standard `virtualenv workon` command.

pipenv/cli.py

@@ -1010,7 +1010,7 @@ def shell(three=None, python=False, compat=False, shell_args=None):
     signal.signal(signal.SIGWINCH, sigwinch_passthrough)
 
     # Interact with the new shell.
-    c.interact()
+    c.interact(escape_character=None)
     c.close()
     sys.exit(c.exitstatus)