Revert "replace dice sanity checks as asserts"

not sure why I would have done this, asserts are not great

This reverts commit b917f78ca5.

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

dice/roller.py

@@ -93,8 +93,12 @@ class DiceRoller(object):
                     size = m[1]
                     if keep > dice or keep == 0:
                         keep = dice
-                    assert size >= 1, f"Die must have at least one side."
-                    assert dice >= 1, f"At least one die must be rolled."
+                    if size < 1:
+                        output = "# of sides for die is incorrect: %d" % size
+                        return output
+                    if dice < 1:
+                        output = "# of dice is incorrect: %d" % dice
+                        return output
                     res = self.roll_dice(keep, dice, size)
                     curr_str += "%d%s" % (res[0], res[1])
                     res = res[0]