[BUG] Line numbers are off in cell evaluation of weave files

[twadleigh]

Steps to reproduce

1. Create a test.jmd file with contents:

```julia
println("This should be line 2 but it is instead line $(@__LINE__).")
```

2. Evaluate the cell and note that it prints:

This should be line 2 but it is instead line 3.

PR to follow.