Build error: sha256sum not found on FreeBSD

[igalic]

error: failed to compile `plume v0.3.0 (/usr/local/src/Plume)`, intermediate artifacts can be found at `/usr/local/src/Plume/target`                                         
                                                                                                                                                                              
Caused by:                                                                                                                                                                   
  failed to run custom build command for `plume v0.3.0 (/usr/local/src/Plume)`                                                                                               
process didn't exit successfully: `/usr/local/src/Plume/target/release/build/plume-e42edb5ba3415496/build-script-build` (exit code: 101)                                     
--- stdout                                                                                                                                                                   
cargo:rerun-if-changed=/usr/local/src/Plume/templates                                                                                                                        
cargo:rerun-if-changed=/usr/local/src/Plume/templates/blogs                                                                                                                  
…etc…
cargo:rerun-if-changed=/usr/local/src/Plume/templates/partials/instance_description.rs.html                                                                                  
cargo:rerun-if-changed=/usr/local/src/Plume/templates/base.rs.html                                                                                                           
cargo:rerun-if-changed=static/css                                                                                                                                            
                                                                                                                                                                             
--- stderr                                                                                                                                                                   
thread 'main' panicked at 'failed sha256sum command: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/libcore/result.rs:999:5stat: illegal option --
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usage: stat [-FLnq] [-f format | -l | -r | -s | -x] [-t timefmt] [file|handle ...]                                                                                           
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.                                                                                               
                                                                                                                                                                             

Since our build already depends on openssl-dev, consider using openssl dgst sha256sum.