Remove prints to stdout when using `--report-json`

[ThoSe1990]

When using --report-json with or without a file creates the prints to stdout. This is unfortunate when piping the output to another program like ./build/bin/example ./examples/features/1_first_scenario.feature --report-json | my-cucumber-consumer

Lets remove all prints to stdout here.

./build/bin/example ./examples/features/1_first_scenario.feature --report-json:

Feature: My first feature  ./examples/features/1_first_scenario.feature:1

Scenario: First Scenario  ./examples/features/1_first_scenario.feature:4
[   PASSED    ] Given An empty box  ./examples/features/1_first_scenario.feature:5
[   PASSED    ] When I place 1 x "apple" in it  ./examples/features/1_first_scenario.feature:6
[   PASSED    ] Then The box contains 1 item  ./examples/features/1_first_scenario.feature:7

Scenario: Alternative Words  ./examples/features/1_first_scenario.feature:9
[   PASSED    ] Given An empty box  ./examples/features/1_first_scenario.feature:10
[   PASSED    ] When I place 1 x "banana" in it  ./examples/features/1_first_scenario.feature:11
[   PASSED    ] Then 1 item is "banana"  ./examples/features/1_first_scenario.feature:12
[   PASSED    ] And I place 1 x "banana" in it  ./examples/features/1_first_scenario.feature:13
[   PASSED    ] Then 2 items are "banana"  ./examples/features/1_first_scenario.feature:14

...here begins the json output now...

[ThoSe1990]

merged #108