Merge pull request #2957 from contradict/fix-docs-exception

Fix an exception during documentation build

Author: ChrisRackauckas

docs/make.jl

@@ -1,4 +1,5 @@
 using Documenter, ModelingToolkit
+using ModelingToolkit: SciMLBase
 
 # Make sure that plots don't throw a bunch of warnings / errors!
 ENV["GKSwstype"] = "100"

docs/src/internals.md

@@ -27,7 +27,7 @@ The procedure for variable elimination inside [`structural_simplify`](@ref) is
 
 ## Preparing a system for simulation
 
-Before a simulation or optimization can be performed, the symbolic equations stored in an [`AbstractSystem`](@ref) must be converted into executable code. This step typically occurs after the simplification explained above, and is performed when an instance of a [`SciMLBase.SciMLProblem`](@ref), such as a [`ODEProblem`](@ref), is constructed.
+Before a simulation or optimization can be performed, the symbolic equations stored in an [`AbstractSystem`](@ref) must be converted into executable code. This step typically occurs after the simplification explained above, and is performed when an instance of a [`SciMLBase.AbstractSciMLProblem`](@ref), such as a [`ODEProblem`](@ref), is constructed.
 The call chain typically looks like this, with the function names in the case of an `ODESystem` indicated in parentheses
 
  1. Problem constructor ([`ODEProblem`](@ref))