update syntax to remove unnecessary underscores after poppy PR 386

[mperrin]

Update to remove now-unnecessary underscores before the [_]get_optical_system function.

Needed to fix failing tests after spacetelescope/poppy#386

[codecov]

Codecov Report

Merging #395 (9d0eabc) into develop (dec015b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #395   +/-   ##
========================================
  Coverage    48.29%   48.29%           
========================================
  Files           14       14           
  Lines         5721     5721           
========================================
  Hits          2763     2763           
  Misses        2958     2958           

Impacted Files	Coverage Δ
webbpsf/wfirst.py	89.77% <ø> (ø)
webbpsf/webbpsf_core.py	78.61% <100.00%> (ø)

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[shanosborne]

It looks like most the the tests have passed. However, the py37-stable test (an allowed failure) did fail though in the same way that the other test envs in 391 are failing

[mperrin]

However, the py37-stable test (an allowed failure) did fail though in the same way that the other test envs in 391 are failing

That makes sense: the stable test cases uses the released stable poppy, so it's inconsistent with the fix here for dev poppy. That test case is an allowed failure precisely for cases like this.

[mperrin]

@shanosborne Are you able & ready to approve this so we can merge? Given that the one allowed failure case in CI is indeed allowed.