Fix ODE subtyping issue

[dkarrasch]

Closes #90.

[codecov-commenter]

Codecov Report

Merging #91 (43823d7) into master (befd910) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   57.25%   57.25%           
=======================================
  Files          17       17           
  Lines        3088     3088           
=======================================
  Hits         1768     1768           
  Misses       1320     1320           

Impacted Files	Coverage Δ
src/pullbacktensors.jl	64.48% <ø> (ø)
src/odesolvers.jl	86.53% <100.00%> (ø)

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