Update quickstart.rst
Update quickstart.rst

Change single "-apiInterface" to "--apiInterface" in example docker launch command. If single dash form is used, the unclear error of "ERROR PID:1 [service.go:37] Failed to start servive: invalid character 'h' looking for beginning of value" is returned on start attempt.
mailgun/vulcand-docs,mailgun/vulcand-docs,mailgun/vulcand,vulcand/vulcand,mailgun/vulcand,vulcand/vulcand-docs,mailgun/vulcand-docs,vulcand/vulcand-docs,vulcand/vulcand,vulcand/vulcand-docs