Upgrade to bitshares 0.1.18

[bitphage]

graphenelib was updated, but dexbot have a dependency on old bitshares 0.1.16 which leads to

Traceback (most recent call last):
  File "./cli.py", line 6, in <module>
    cli.main()
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/vvk/devel/DEXBot/dexbot/ui.py", line 128, in new_func
    return ctx.invoke(f, *args, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/vvk/devel/DEXBot/dexbot/ui.py", line 81, in new_func
    **ctx.obj
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/bitshares-0.1.16-py3.6.egg/bitshares/bitshares.py", line 144, in __init__
    **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/bitshares-0.1.16-py3.6.egg/bitshares/bitshares.py", line 173, in connect
    self.rpc = BitSharesNodeRPC(node, rpcuser, rpcpassword, **kwargs)
  File "/home/vvk/.local/share/virtualenvs/DEXBot-XTl2tJdV/lib/python3.6/site-packages/bitshares-0.1.16-py3.6.egg/bitsharesapi/bitsharesnoderpc.py", line 24, in __init__
    self.chain_params = self.get_network()
AttributeError: can't set attribute