fix: set height of lti modal to 100% not auto

[ilee2u]

TICKET: https://2u-internal.atlassian.net/browse/COSMO-227

It seems the css for the height of an LTI modal's iframe was set to "auto" (which seemed to be defaulting to 100vh), not 100%, which seems to have caused issues for some learners on iPads.

NOTE: I have yet to test this locally and I'm not sure I can, especially given that we can't use the IMS global to anymore.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.83%. Comparing base (1de6fa7) to head (e9bb1b2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #460   +/-   ##
=======================================
  Coverage   97.83%   97.83%           
=======================================
  Files          77       77           
  Lines        6710     6710           
=======================================
  Hits         6565     6565           
  Misses        145      145           

Flag	Coverage Δ
unittests	97.83% <ø> (ø)

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