Incremental compilation may be broken for this module?

I'm using `Calculus.jl` in `FEMBasis.jl` to calculate partial derivatives of interpolation polynomials symbolically before code generation. During precompilation of package, I get a lot of following messages:

```
WARNING: eval from module Calculus to FEMBasis:
Expr(:call, :*, 0.5, 1)
** incremental compilation may be broken for this module **
WARNING: eval from module Calculus to FEMBasis:
Expr(:call, :*, 0.5, 1)
** incremental compilation may be broken for this module **
WARNING: eval from module Calculus to FEMBasis:
Expr(:call, :*, -0.5, 1)
** incremental compilation may be broken for this module **
# ... continues thousands of lines ...
```

For whole build log, see https://travis-ci.org/JuliaFEM/FEMBasis.jl/jobs/418381139.

Here's the lines I use Calculus:

- https://github.com/JuliaFEM/FEMBasis.jl/blob/master/src/create_basis.jl#L25
- https://github.com/JuliaFEM/FEMBasis.jl/blob/master/src/create_basis.jl#L38

Is this issue of FEMBasis or Calculus and how to solve this, or should I even be worried about this..?