fix(pip): fix pip version to 19.3

This fix is needed to avoid jurko error:

Collecting suds-jurko==0.6 (from -r requirements.txt (line 39))
  Using cached suds-jurko-0.6.zip (255 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [1 lines of output]
      error in suds-jurko setup command: use_2to3 is invalid.
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error