Replaced EOL dashing with foxy in example

[chriseichmann]

The simple example in the Usage Section of the readme no longer succeeds due to rosdep errors (dashing reached its EOL, making it a non-trivial example).

I've changed the targeted rosdistro for the example to foxy.

[christophebedard]

LGTM! Could you just sign-off your commit so that the DCO check passes?

[codecov[bot]]

Codecov Report

Merging #329 (1574f72) into master (56392b7) will decrease coverage by 0.15%. The diff coverage is n/a.

:exclamation: Current head 1574f72 differs from pull request most recent head d2a30e3. Consider uploading reports for the commit d2a30e3 to get more accurate results

@@            Coverage Diff             @@
##           master     #329      +/-   ##
==========================================
- Coverage   93.23%   93.08%   -0.16%     
==========================================
  Files          11       11              
  Lines         414      405       -9     
==========================================
- Hits          386      377       -9     
  Misses         28       28              

Flag	Coverage Δ
unittests	93.08% <ø> (-0.16%)	:arrow_down:

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Impacted Files	Coverage Δ
ros_cross_compile/pipeline_stages.py	93.33% <0.00%> (-0.79%)	:arrow_down:
ros_cross_compile/data_collector.py	96.66% <0.00%> (-0.06%)	:arrow_down:
ros_cross_compile/platform.py	100.00% <0.00%> (ø)

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