docker/dockerfile:Updated dockerfile

[sladyn98]

With the recent update to pip 19.01 there was a build slight issue with the docker commands, refer here: https://github.com/pypa/pip/issues/6197, which has been fixed.

[sladyn98]

Yeah I think that would be the best option since the docker will complain.Do you want me to edit and submit a PR again?

[coveralls]

Pull Request Test Coverage Report for Build 1128

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 33 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.08%) to 70.936%

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Files with Coverage Reduction	New Missed Lines	%
conpot/protocols/ftp/ftp_base_handler.py	4	80.12%
conpot/protocols/http/command_responder.py	5	54.32%
conpot/protocols/ftp/ftp_handler.py	10	80.31%
conpot/protocols/IEC104/IEC104_server.py	14	47.31%
<!--	Total:	33		-->

Totals
Change from base Build 1126:	-0.08%
Covered Lines:	5367
Relevant Lines:	7566

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💛 - Coveralls

[xandfury]

Thanks for your contribution :heart: