Fix for build docker image | wrong pip version

[volekerb]

RUN pip3 triggers pip 3.6 version but not 3.7 and dependencies could be installed with an error:

Step 9/11 : RUN pip3 install -e .
 ---> Running in be35c386c2b8
Obtaining file:///neo-python
neo-python requires Python '>=3.7' but the running Python is 3.6.8
The command '/bin/sh -c pip3 install -e .' returned a non-zero code: 1

What current issue(s) does this address, or what feature is it adding?

How did you solve this problem?

How did you make sure your solution works?

Are there any special changes in the code that we should be aware of?

Please check the following, if applicable:

• [ ] Did you add any tests?
• [ ] Did you run make lint?
• [ ] Did you run make test?
• [ ] Are you making a PR to a feature branch or development rather than master?
• [ ] Did you add an entry to CHANGELOG.rst? (if not, please do)

[coveralls]

Coverage remained the same at 85.307% when pulling 834b27ba38fd29efc7dba9b10fbf6ac79c216505 on volekerb:patch-1 into 5bdded2c339219355cf1d31ae58653b0f94c6e51 on CityOfZion:master.

[volekerb]

created correct PR #1011