Fix error message mentionning graphicsmagick instead of imagemagick

[nicoulaj]

The error message mentions graphicsmagick, but the program actually calls convert which is provided by imagemagick.
You can have graphicsmagick "installed as imagemagick" (eg: https://aur.archlinux.org/packages/graphicsmagick-imagemagick-compat/), but I think it would be less confusing just mentionning imagemagick.

[phiresky]

oh. yeah that was because I used to have it use graphicsmagick (cuz much faster usually) but then I had some problem with that. Thanks!

[giovannibonetti]

On the other hand, when running the command like this...

rga something -g '*.pdf' --rga-adapters=+pdfpages,tesseract

...I get a warning that says gm is required:

-------------------------------------------------------------------------------
Warning: found multiple adapters for my-pdf-file.pdf:
 - pdfpages
 - poppler
adapter: pdfpages
Error: Could not find executable "gm". Make sure you have imagemagick installed.
-------------------------------------------------------------------------------

After installing graphicsmagick the warning disappeared and everything worked fine.
Running on macOs Catalina v10.15.4

[phiresky]

Huh, now I'm confused. Looks like it does use gm after all:

        let exe_name = "gm";
        let mut cmd = Command::new(exe_name);
        cmd.arg("convert")
            .arg("-density")
            .arg("200")
            .arg(inp_fname)
            .arg("+adjoin")
            .arg(out_fname);

Maybe @nicoulaj misread the code (like I did when looking again before merging the PR)? But then why did they submit this at all, did it show some different issue without having imagemagick installed?