fix error when x is a ndarray

[huanglangwen]

Fix error in https://github.com/JuliaDiffEq/OrdinaryDiffEq.jl/blob/master/test/interface/ode_twodimlinear_tests.jl#L23

[ChrisRackauckas]

Can this get a test?

[coveralls]

Coverage decreased (-7.2%) to 61.714% when pulling 778c332 on oop into 5441342 on master.

[codecov]

Codecov Report

Merging #77 into master will increase coverage by 0.63%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
+ Coverage   73.38%   74.02%   +0.63%     
==========================================
  Files           8        8              
  Lines         496      512      +16     
==========================================
+ Hits          364      379      +15     
- Misses        132      133       +1

Impacted Files	Coverage Δ
src/jacobians.jl	89.93% <90%> (+0.42%)	⬆️

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[ChrisRackauckas]

Awesome!