Fix hpx interface

[omodei]

fix interface to new gammapy

[codecov]

Codecov Report

Attention: Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.

Project coverage is 49.65%. Comparing base (00a7fc5) to head (d7ca78c).

Files with missing lines	Patch %	Lines
fermipy/plotting.py	16.66%	5 Missing ⚠️
fermipy/gtanalysis.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #608   +/-   ##
=======================================
  Coverage   49.65%   49.65%           
=======================================
  Files         143      143           
  Lines       27191    27190    -1     
=======================================
  Hits        13502    13502           
+ Misses      13689    13688    -1     

Flag	Coverage Δ
unittests	49.65% <14.28%> (+<0.01%)	⬆️

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