Use read-shell-command instead of read-from-minibuffer (#60)

…when prompting for pytest command when prompting for pytest command.

The primary advantage of this is that tab completion completes from files in
the CWD, which is much more useful for pytest (where test files are valid
arguments).

python-pytest.el

@@ -356,9 +356,9 @@ With a prefix ARG, allow editing."
       (setq edit (not edit)))
     (when edit
       (setq command
-            (read-from-minibuffer
+            (read-shell-command
              "Command: "
-             command nil nil 'python-pytest--history)))
+             command 'python-pytest--history)))
     (add-to-history 'python-pytest--history command)
     (setq python-pytest--history (-uniq python-pytest--history))
     (puthash (python-pytest--project-root) command