handle lack of matrix syntax on julia v1.6

Author: baggepinnen

src/systems/abstractsystem.jl

@@ -1096,6 +1096,9 @@ See also [`linearization_function`](@ref) which provides a lower-level interface
 
 See extended help for an example.
 
+The implementation and notation follows that of
+["Linear Analysis Approach for Modelica Models", Allain et al. 2009](https://ep.liu.se/ecp/043/075/ecp09430097.pdf)
+
 # Extended help
 This example builds the following feedback interconnection and linearizes it from the input of `F` to the output of `P`.
 ```

test/linearize.jl

@@ -73,7 +73,7 @@ desired_order = [f.x, p.x]
 lsys = ModelingToolkit.reorder_states(lsys, states(ssys), desired_order)
 
 @test lsys.A == [-2 0; 1 -2]
-@test lsys.B == [1; 0;;]
+@test lsys.B == reshape([1; 0;;], 2, 1) # reshape required when testing on Julia v1.6
 @test lsys.C == [0 1]
 @test lsys.D[] == 0